A newcomer’s first loss in DeFi is often not a market loss. It comes from an operation: a transfer sent on the wrong network, an unlimited approval granted to a contract they never checked, a fake support agent who asked for twelve words, a site that looked like the real one. DeFi for beginners is less about yields and protocols than about six habits that keep those mistakes away.
This lesson is a checklist and a test. It assumes you have read our introduction to decentralised finance, which explains lending, exchanges and the rest; nothing here defines DeFi again. Instead, each section recalls one thing you should already know from the blockchain course, links to the lesson that teaches it in full, and adds what changes when a DeFi app is on the other side of the screen.
At the end there are ten questions with their answers. Nine or ten right and you have the basics. Fewer, and the answers tell you which lesson to reopen.
DeFi for beginners: six things to know before your first transaction
Before you connect a wallet to any DeFi app, you should be able to say where your keys are and who else could use them, what a network fee is and why you pay it even when a transaction fails, what a smart contract can do with your tokens once you approve it, how to read a transaction on a block explorer, what backs the stablecoin you are about to deposit, and which network you are on, with its own gas token.
None of this asks for code or maths beyond a multiplication. It asks for attention at the moment you sign. A DeFi app has no account manager and no reset button: the contract does what the transaction says, and the transaction says what you approved.
A second point surprises people coming back after a few years away. On 27 October 2026, sending ETH on Ethereum mainnet cost a fraction of a cent (the dated figures are below). So the question of how much you need to begin is no longer mainly about the cost of a transfer. It depends on what you do with the money (swaps, approvals, bridges) and on how fast fees can climb when the network is busy.
Wallets and keys: the app shows your tokens, the chain holds them
A wallet, in the words of ethereum.org’s wallet page, is an app or a device that lets you hold, send and receive ETH and other tokens and sign in to apps. The tokens are not inside the app. They are recorded on the blockchain against an account, which is a pair of keys; the wallet uses those keys to show your balance and to sign what you send. That is why the same twelve or twenty-four words can restore the account in a different wallet app on a different phone.
The consequence for DeFi is direct. Wallet providers do not hold your funds, so they cannot freeze them for you, refund them or recover them. Nobody runs a help desk for a self-custody wallet. A centralised exchange is the opposite case: it holds the coins for you, which brings its own risk, the risk of the exchange itself. Most DeFi apps only work with the first kind, a wallet whose keys you control. Our guide to crypto wallets compares the types, and the lesson on private and public keys shows why whoever holds the private key controls the account.
The recovery phrase is the master copy. Ethereum.org advises writing it down and keeping it off any computer, because it is the only way back into the account if the phone or device is lost. Its security page goes further: “No legitimate service, support agent, or website will ever ask you for these.” The details of storage (paper, metal, several copies, where not to keep it) are in our lesson on seed phrase security.
Hot wallets live on a connected phone or browser; hardware wallets keep the keys on a separate device that signs without exposing them. The same ethereum.org page says hardware wallets are considered the most secure option for storing private keys. One common setup is a small hot wallet for daily use and a hardware wallet for the rest, so that a bad signature in the browser cannot reach everything.
Gas: you pay for every action, even a failed one
Every action on Ethereum, from a plain transfer to a deposit in a lending pool, is a transaction, and every transaction pays a fee. Ethereum’s documentation on gas defines gas as the unit that measures the computational effort an operation needs. The fee is paid in ETH and quoted in gwei, a billionth of one ETH.
The formula is short: the fee equals the gas units used multiplied by the sum of the base fee and the priority fee (the tip). The protocol sets the base fee from demand and burns it; the tip goes to the validator that includes your transaction. Your wallet also sets a maximum fee per unit of gas, higher than base fee plus tip, and the difference is refunded. A standard ETH transfer to an ordinary address needs 21,000 units of gas. A swap or a deposit runs code in one or several contracts, so it uses several times that.
The rule that surprises beginners: a failed transaction still costs money. The documentation is plain that “the fee is paid regardless of whether a transaction succeeds or fails.” If a transaction runs out of gas, its changes are reverted, yet “all the gas provided will still be consumed for the work performed.” Only gas that a successful transaction did not need comes back to you. Our lesson on how crypto transactions work follows a transaction from signature to block, and the glossary entry on gas fees gives the short version.
Gas on 27 October 2026: a dated example
Here is what the numbers looked like on the morning of this lesson. Treat them as a snapshot taken at one moment, not as a price list: they change from block to block. Reading the blocks themselves, the Ethereum base fee moved between about 0.055 and 0.069 gwei from 09:43 to 09:49 UTC that morning, so even within six minutes the figure was not fixed.
| Item (27 October 2026) | Value | Source and time (UTC) |
|---|---|---|
| Ethereum mainnet base fee | 0.059 gwei | Etherscan gas tracker, 09:46 |
| Etherscan “high” gas price | 0.066 gwei | Etherscan gas tracker, 09:46 |
| Priority fee for a “rapid” transaction | 0.007 gwei | Etherscan gas tracker, 09:46 |
| ETH/USD reference price | about $2,306 | Chainlink ETH/USD oracle on Ethereum, updated 09:42 |
| Plain ETH transfer at 0.059 gwei | 0.000001239 ETH, about $0.003 | Coindaro arithmetic from the rows above |
| Base gas price (layer 2, execution only) | 0.006 gwei | public RPC node, around 09:46 |
| Arbitrum One gas price (layer 2, execution only) | 0.020 gwei | public RPC node, around 09:46 |
| OP Mainnet gas price (layer 2, execution only) | 0.001 gwei | public RPC node, around 09:46 |
The transfer row is simple arithmetic: 21,000 gas multiplied by 0.059 gwei gives 1,239 gwei, or 0.000001239 ETH. At about $2,306 per ETH, the reference price the Chainlink ETH/USD feed reported at 09:42 UTC that day (an oracle reading, not an exchange quote), that is roughly three tenths of a cent. The standard priority fee shown by Etherscan was zero, so the base fee alone sets the cost. At Etherscan’s “high” level of 0.066 gwei it comes to 1,386 gwei, still well under a cent. The figures come from the Etherscan gas tracker at 09:46 UTC.
The three layer-2 rows need care. They are the gas prices each network reported, but on a layer 2 you also pay a share of the cost of posting your transaction’s data to Ethereum, and that part is not in the figure. So they show that layer-2 execution was cheaper still; they do not give a dollar cost per transaction, and this lesson does not turn them into one.
Why the fee you saw today is not the fee you will pay
The base fee follows demand for block space. When many people want to transact at once (a market crash, a popular token launch, a big airdrop claim) it rises, sometimes very fast, and the cost of the same swap can be many times higher an hour later. A fee of a fraction of a cent is a fact of 27 October 2026, not a property of Ethereum.
The type of action matters as much as the moment. An approval, a swap routed through several pools, a deposit followed by a borrow: each one is a separate transaction with its own gas. A beginner who plans to try three apps in an afternoon should count the approvals as well as the actions, and the revokes later on. Your wallet shows an estimate before you sign; read it, and cancel if it is out of proportion with the amount you are moving.
Smart contracts and dApps: code that cannot be called back
Ethereum’s developer documentation puts it simply: “A ‘smart contract’ is simply a program that runs on the Ethereum blockchain.” It is code and data stored at an address. Anyone can call it by sending a transaction, and anyone can deploy one by paying gas, without asking permission. A DeFi app is a website that prepares those transactions for you; the website can change or vanish, the contract stays. Our guide to dApps explains the split between the front end and the code on chain.
The same page adds the sentence every DeFi user should keep in mind: “Smart contracts cannot be deleted by default, and interactions with them are irreversible.” If you deposit into the wrong contract or approve the wrong one, there is no network operator to call. Once a transaction is finalised on Ethereum it cannot be undone in practice.
Irreversible does not always mean unchangeable. Ethereum’s page on upgrading contracts explains that contracts are immutable by design, but many teams deploy them behind a proxy: the address stays the same while the logic behind it can be swapped for a new version. That is useful for fixing bugs, and it means trusting whoever holds the upgrade rights. Restricting those rights, sharing them in a multisig wallet, putting changes to a DAO vote or delaying them with a timelock are the usual safeguards. Before depositing, look for which of them the protocol uses; its documentation or audit reports usually say.
Bugs are the other side of public code. Ethereum.org’s DeFi page notes that these products, like any software, can suffer from bugs and exploits. Code that anyone can read can also be studied by attackers, and contracts that hold large sums are the ones they study first. Audits reduce that risk without removing it.
ERC-20 tokens and approvals: what you let an app spend
Most of what a DeFi app handles is not ETH but tokens: stablecoins, governance tokens, receipts for deposits. Nearly all of them follow ERC-20, the standard for fungible tokens proposed by Fabian Vogelsteller in November 2015. ETH is the native coin of the network; an ERC-20 token is a balance kept by a contract. Our lesson on coins and tokens covers the difference.
Two details of the standard matter in DeFi. The first is decimals: a contract stores balances as whole numbers and tells wallets how many decimal places to show, which is why a token amount can look odd in an explorer before it is converted. The second is the approval mechanism. A DeFi contract cannot simply take your tokens. You first call approve, which sets an allowance: how much a given contract may move from your address. The app then uses transferFrom to pull up to that amount, and allowance shows what is left.
Many apps ask for an unlimited allowance so you do not have to approve again next time. That is convenient, and it means the contract can move all of that token from your address, now and later, for as long as the approval stands. Ethereum.org’s security page warns that an unlimited spend could let the contract drain your wallet. If the contract is later exploited, or if the site was a copy of the real one, the allowance is what the attacker uses.
Checking and revoking approvals
Approvals do not expire, and ethereum.org’s guide to revoking token access points out that disconnecting your wallet from a website does not remove them. To see and cancel them, the guide names several tools: Etherscan’s token approval checker, Blockscout’s revoke page, Revoke.cash (which covers several networks), Unrekt and EverRevoke. Revoking is itself a transaction, so it costs gas.
Revoking an approval does not close a deposit, a stake or a loan you hold in that protocol; it only stops the contract from pulling more of that token. A sensible routine for a beginner is to set the allowance to the amount actually needed when the wallet offers the choice, and to review approvals once a month or after trying a new app.
Block explorers show what really happened
A wallet tells you what it thinks happened. A block explorer shows what the chain recorded. Ethereum.org describes explorers as a portal to Ethereum’s data, and the list of what they display is long: for a transaction, its hash, its status (pending, failed or successful), the block and time, the sender and recipient, the tokens moved, the value and the fee; for an account, its balances and history; for a contract, its creator and, when the developers verified it, its source code and interface; for a token, its supply, holders and decimals.
Etherscan is the best known for Ethereum. Blockscout, Blockchair, Otterscan, OKLink and Ethplorer are among the alternatives ethereum.org lists, and Beaconcha.in shows the validator side of the network. Layer-2 networks have their own explorers, often run on the same software.
An explorer earns its place on both sides of a DeFi action. Before you deposit, paste the contract address the app shows into the explorer and check that it is the protocol’s official contract (the address from its documentation, not from a social media post). After you sign, open the transaction hash and confirm the status is successful and that the tokens went where you expected. When something looks wrong, the explorer is also where you can see whether a pending transaction is still waiting in the queue or already failed, and what fee it burned.
Stablecoins: the dollar tokens most DeFi runs on
Many DeFi apps work with stablecoins, tokens meant to hold a steady value, usually one dollar. They are not all built the same way, and ethereum.org’s stablecoin page sorts them into four kinds. Fiat-backed stablecoins such as USDC and USDT are issued by a company that holds reserves; you rely on that issuer and on audits of its reserves. Crypto-backed ones such as USDS use other crypto assets as collateral, overcollateralised to absorb price moves; if the collateral falls, more of it is needed to keep the backing. Ethereum.org also files Ethena’s USDe in this group, but its design differs: Ethena’s documentation pairs its volatile crypto backing with short futures positions of about the same size, which offsets price moves instead of piling up extra collateral. Some track precious metals, such as Pax Gold and Tether Gold. Algorithmic stablecoins are not backed by any other asset and depend on their mechanism working.
For a beginner, the useful question before a deposit is plain: what would make this token worth less than a dollar, and who would I be relying on? Our guide to stablecoins goes through the models and their failures, including what happens when one loses its peg.
Layer 2 networks: cheaper, but check where you are
Many DeFi apps also run on layer-2 networks that post their data to Ethereum, such as Arbitrum, Base and OP Mainnet. They are cheaper to use, as the table above suggests, and each is a separate network with its own addresses for the same tokens, its own explorer and its own balance of ETH for gas. Our lesson on layer 1 and layer 2 explains how they inherit Ethereum’s security.
The traps are practical. A wallet can show you on one network while the app expects another, so check the network name before you sign. You also need the gas token of the network you are on: USDC on Arbitrum with no ETH on Arbitrum cannot move. And coming back to Ethereum takes time on some networks. On an optimistic rollup, ethereum.org explains, a withdrawal by the official route waits for a challenge period of roughly seven days, during which anyone can dispute the rollup’s results. Liquidity providers offer faster exits: they pay you on Ethereum right away, for a fee, and wait out the period themselves. Zero-knowledge rollups work differently, so check the network’s own documentation.
Practice is free. Ethereum’s page on networks recommends the Sepolia test network for trying applications and contracts; test ETH comes from faucets and is meant to have no real value. Hoodi is the testnet for validators and protocol upgrades, and Holesky was deprecated in September 2025. When an app offers a testnet version, a first swap there costs nothing and teaches the same screens.
Scams and signatures: the traps of a first week
Ethereum.org’s security page is blunt about the commonest lure: “Giveaways are always scams.” Send one ETH and get two back, a free token for the first thousand wallets, a celebrity live stream with a QR code: the pattern is old and still works. The second classic is the support agent who contacts you first, on Discord, Telegram or X, offers to fix a problem and ends by asking for your recovery phrase or for you to connect to a “validation” site.
The third is quieter and more dangerous in DeFi: a copy of a real app, reached through a sponsored search result, a fake airdrop or a message, that asks for a signature. The transaction looks routine, but it is an unlimited approval to the attacker’s contract, or a signed permission that lets it move your tokens later. Ethereum.org’s advice is to read what you are signing before you sign it, and to set spend limits rather than leave them unlimited. If the wallet shows a request you do not understand, reject it; nothing on chain happens until you confirm.
Bookmark the addresses of the few apps you use and open them from the bookmark, never from a link. Treat any message that creates urgency (“your wallet will be suspended”, “claim within the hour”) as a red flag. Our guide to avoiding crypto scams lists the main schemes and what to do if you have already signed something.
Self-test: ten questions on DeFi basics
Write your answers down before you scroll to the next section. Each question matches one section of this lesson; the gas figures in question 4 are those of 27 October 2026.
- Your self-custody wallet app shows 0.5 ETH and 200 USDC. Where are these assets actually held: (a) inside the app on your phone, (b) on the blockchain, tied to your key pair, or (c) with the company that makes the wallet?
- Someone presenting as wallet support writes to you on social media and asks for your twelve recovery words to “verify” your account. What do you do?
- Your DeFi transaction shows “failed” on the explorer. Did you pay a fee?
- A plain ETH transfer uses 21,000 gas. On 27 October 2026 at 09:46 UTC (a snapshot from the Etherscan gas tracker) the base fee was 0.059 gwei, the standard priority fee was zero and the Chainlink oracle priced ETH at about $2,306. Roughly what did the transfer cost at that moment, in ETH and in dollars?
- You sent tokens to a smart contract by mistake. Can the network reverse it? And can the developers change the contract’s code?
- A DeFi app asks you to approve a token for an unlimited amount. What exactly have you allowed, and does the permission end when you disconnect your wallet from the site?
- How can you check, without trusting the app or your wallet, whether a transaction succeeded and where the tokens went?
- Which kind of stablecoin depends on the price of other crypto assets and is overcollateralised: (a) fiat-backed, like USDC, (b) crypto-backed, like USDS, or (c) algorithmic?
- You withdraw from an optimistic rollup to Ethereum mainnet by the official bridge. Roughly how long can it take, and how do some users get their funds sooner?
- You want to try a swap and a deposit without risking any money. What do you use?
Answers and explanations
- Answer (b). The assets are recorded on the blockchain against your account, which is a key pair; the app uses the keys to display and sign. Wallet providers do not hold your funds, so if you lose the keys and the recovery phrase, nobody can restore access. Missed it? Reopen the guide to crypto wallets.
- You give nothing and stop the conversation. No legitimate service or support agent ever asks for a recovery phrase, and anyone who has it controls the account. Report the account if the platform allows it. Missed it? Reopen the lesson on seed phrase security.
- Yes. A transaction that fails during execution is still included in a block, its changes are reverted and the gas it used is paid, because validators did the work. Only a transaction that never gets included costs nothing. Missed it? Reopen the section on gas above.
- About 0.000001239 ETH, roughly $0.003. The calculation is 21,000 multiplied by (0.059 gwei of base fee plus a zero tip), which gives 1,239 gwei; one gwei is a billionth of an ETH, and 0.000001239 ETH at $2,306 is about $0.0029. That was the level of one morning: with the base fee ten or a hundred times higher, the cost rises in proportion. Missed it? Reopen the dated example in the gas section.
- No reversal: interactions with smart contracts are irreversible and the network has no one to undo them. The code cannot be changed either, unless the contract was deployed behind an upgrade proxy; then whoever holds the upgrade rights can switch the logic, which is why multisigs and timelocks matter. Missed it? Reopen the guide to dApps.
- You have allowed that contract to move all of that token from your address, now and later. The approval does not expire and disconnecting the wallet from the website does not remove it; you revoke it with a tool such as Revoke.cash or Etherscan’s approval checker, in a transaction that costs gas. Missed it? Reopen the section on approvals above.
- With a block explorer such as Etherscan or Blockscout. Paste the transaction hash: it shows the status (pending, failed or successful), the sender, the recipient, the tokens moved and the fee. Missed it? Reopen the section on block explorers above.
- Answer (b). Crypto-backed stablecoins hold more collateral than the tokens they issue because that collateral moves in price; if it falls, more is needed to keep the backing. Fiat-backed ones depend on an issuer’s reserves, and algorithmic ones have no backing asset at all. (Ethena’s USDe, sometimes placed in the same family, relies on a hedge with short futures rather than on overcollateralisation.) Missed it? Reopen the guide to stablecoins.
- Roughly seven days, the challenge period during which anyone can dispute the rollup’s results. Some users pay a liquidity provider, which sends them funds on Ethereum at once for a fee and waits out the period in their place. Missed it? Reopen the lesson on layer 1 and layer 2.
- A public test network such as Sepolia, with free test ETH from a faucet. Test ETH is meant to have no real value, so mistakes cost nothing; just make sure your wallet is on the testnet and not on mainnet when you practise. Missed it? Reopen the section on layer-2 networks and testnets above.
Nine or ten right answers: you have the basics this course assumes, and you can move on. Six to eight: reread the lessons named under the answers you missed before connecting a wallet to a real app. Below six: start again with wallets and keys, the base on which everything else rests.
Network fees, not a fixed rule, set the minimum to start
The first question in any talk about DeFi for beginners is how much money it takes. There is no official minimum. A protocol does not ask for a deposit threshold the way a bank account might; what sets a practical floor is the fees. If a deposit, an approval and a later withdrawal together cost more than a meaningful share of what you move, the operation makes little sense. On 27 October 2026 those fees were tiny on Ethereum mainnet and smaller still on layer 2s, as the table above shows, but a busy day can change that within hours.
Some costs are easy to forget. The bridge or the exchange withdrawal that brings funds onto a layer 2 has its own fee. Each new app needs at least one approval. And getting out (withdrawing, swapping back, revoking) costs as much as getting in. Add them up with your wallet’s estimates before the first deposit rather than after.
The other limit is personal. DeFi is a risky area where code can fail and where, as the next section shows, protection is thinner than at a regulated broker. Only you can decide what amount you could lose without harm; this lesson does not suggest one, and money borrowed for the purpose turns a lesson into a debt. The cheapest first step remains a testnet: the same apps, the same signatures, no value at stake.
What the IRS and the SEC have said, for US readers
For tax, the IRS digital assets page (last reviewed on 2 September 2026) treats digital assets, stablecoins included, as property, not currency. Form 1040 asks a yes-or-no question about digital assets. You can answer no if you only held them, bought them with dollars or moved them between your own wallets, unless you paid a fee in a digital asset. You answer yes if you received rewards or staking income, disposed of a digital asset for another one, for dollars or for goods, or paid a transfer fee in a digital asset. Applied to DeFi, that list catches the swap of one token for another and the gas paid in ETH, which the page names in so many words for fees. Our guide to US crypto taxes covers forms and calculations.
On regulation, at a Securities and Exchange Commission Crypto Task Force roundtable on DeFi on 9 June 2025, Chairman Paul Atkins said, in what his published remarks present as his own views rather than the Commission’s, “I am in favor of affording greater flexibility to market participants to self-custody crypto assets”. He also said he had asked SEC staff to consider a conditional exemptive framework, an “innovation exemption”, for on-chain products. A speech is not a rule: in the same remarks he noted that a staff statement on mining and staking is not a rule with the force of law. A friendlier tone does not create investor protection: a DeFi protocol usually has no compensation scheme behind it.
Tax and regulation differ by country; the checks of the self-test do not. A later lesson of this path tells how decentralised finance grew from the launch of the Dai stablecoin in December 2017 into today’s market, and which failures along the way gave rise to those checks.
