Web3 Tutorial: Learn Decentralized Web from Scratch (2026)
Web3 is a vision of the internet where users own their data, identity, and digital assets — mediated by blockchains, not corporate servers. After building a decentralized marketplace and a DAO voting app, I can say the technology is real but the usability gap is still wide. This tutorial cuts through the jargon to show you how to build decentralized applications (dApps) that actually work.
You will learn how wallets interact with smart contracts, how IPFS stores content permanently, how to authenticate users without passwords, and the security patterns that prevent your users from losing funds.
Wallets, RPCs, and Providers
A Web3 application replaces the database with a blockchain and the user account with a wallet. The wallet (MetaMask, WalletConnect) manages private keys and signs transactions. The provider (ethers.js or web3.js) communicates with an RPC endpoint (Infura, Alchemy, or your own node) to read and write blockchain state.
When a user connects their wallet, the dApp gets access to the user's address and can request signed messages or transactions. Crucially, the dApp never holds the private key — the user signs everything in their wallet. This means users can interact with your app without creating an account or trusting your server.
import { ethers } from 'ethers';
const provider = new ethers.BrowserProvider(window.ethereum);
const signer = await provider.getSigner();
const address = await signer.getAddress();
console.log(`Connected: ${address}`);
const contract = new ethers.Contract(
'0x...',
['function balanceOf(address) view returns (uint256)'],
provider
);
const balance = await contract.balanceOf(address);Smart Contract Interaction
Reading data from a smart contract is free — it requires no gas because the node executes the call locally without submitting a transaction. Writing requires a signed transaction with gas. The client sends the transaction, waits for a receipt, and then updates the UI.
Events are the primary way dApps track what happened. A contract emits events which are indexed in the blockchain's logs. Clients subscribe to events using provider.on(eventName, callback) for real-time updates, avoiding polling.
const tx = await contract.mint({
value: ethers.parseEther('0.1')
});
const receipt = await tx.wait();
console.log(`Minted in block ${receipt.blockNumber}`);
contract.on('Transfer', (from, to, amount, event) => {
console.log(`Transfer: ${from} -> ${to}: ${ethers.formatEther(amount)} ETH`);
});Decentralized Storage with IPFS
Storing large files on a blockchain is prohibitively expensive. IPFS (InterPlanetary File System) provides content-addressed, peer-to-peer file storage. Files are identified by their cryptographic hash (CID), so the same file always produces the same CID. Pinning services (Pinata, Web3.Storage) ensure your files stay available even when your local node is offline.
The common pattern: store metadata and file URLs on-chain (as IPFS CIDs), and the actual content off-chain on IPFS. For NFT metadata, this is the ERC-721 standard: the tokenURI points to an IPFS JSON file.
import { create } from 'ipfs-http-client';
const ipfs = create({ url: 'https://ipfs.infura.io:5001' });
async function uploadMetadata(name, description, imagePath) {
const imageResult = await ipfs.add(await fs.readFile(imagePath));
const metadata = {
name,
description,
image: `ipfs://${imageResult.path}`
};
const metadataResult = await ipfs.add(JSON.stringify(metadata));
return `ipfs://${metadataResult.path}`;
}Sign-In with Ethereum
SIWE (EIP-4361) lets users authenticate to web applications using their Ethereum wallet instead of a password. The user signs a standardized message with their private key. The server verifies the signature, extracts the address, and issues a session token.
This replaces the traditional email/password flow. The advantages: no password hashing, no credential storage on your server, phishing resistance (the signed message includes the domain), and portability — users carry their identity across applications using the same wallet.
const message = `${domain} wants you to sign in with your Ethereum account:\n${address}\n\nSign in to MyApp\n\nURI: ${origin}\nVersion: 1\nNonce: ${nonce}\nIssued At: ${new Date().toISOString()}`;
const signature = await signer.signMessage(message);
import { SiweMessage } from 'siwe';
const siwe = new SiweMessage(message);
const { address } = await siwe.verify({ signature });Building a DAO
A DAO (Decentralized Autonomous Organization) is a smart contract that manages shared funds based on member votes. Members hold governance tokens and propose actions. If a proposal passes (quorum + majority), the contract executes the action — typically transferring ETH or calling another contract.
OpenZeppelin's Governor contract provides a battle-tested framework: members delegate voting power, create proposals with executable calldata, vote during a voting period, and execute after the timelock expires.
import "@openzeppelin/contracts/governance/Governor.sol";
contract MyDAO is Governor, GovernorSettings, GovernorCountingSimple, GovernorVotes, GovernorTimelockControl {
constructor(IVotes _token, TimelockController _timelock)
Governor("MyDAO")
GovernorSettings(1, 50400, 100 ether)
GovernorVotes(_token)
GovernorTimelockControl(_timelock)
{}
}Web3 Security
Web3 security is asymmetric: one mistake can drain a user's entire wallet. The most common attacks on dApps include: phishing sites that fake the dApp UI and ask for seed phrases, approval scams (unlimited token approvals), and malicious frontends that inject different contract addresses.
Best practices: never ask for a seed phrase, use limited token approvals (approve exact amounts, not uint256.max), verify the contract address on Etherscan before interacting, and always simulate transactions before signing.
const USDT = new ethers.Contract(usdtAddress, ['function approve(address, uint256) external'], signer);
const tx = await USDT.approve(contractAddress, swapAmount);
await tx.wait();
const code = await provider.getCode(contractAddress);
if (code === '0x') {
throw new Error('No contract at this address');
}Frequently Asked Questions
Do I need a blockchain to build a Web3 app?
Yes, the blockchain is the backend. However, not every part needs to be on-chain. Use a traditional database for search indexing, user preferences, and cached data. Only the core trust-critical logic belongs on-chain.
How do I handle gas costs for my users?
Gasless transactions use a relayer: users sign a typed message, and your backend submits it and pays the gas. Biconomy and OpenZeppelin Defender provide relayer services. EIP-2771 (meta-transactions) is the standard for this.
What happens if the user loses their wallet?
Without seed phrase recovery, the wallet is unrecoverable — that is the trade-off for self-custody. Social recovery (Argent wallet) and MPC wallets offer recovery mechanisms. Always warn users to back up their seed phrase offline.
Is Web3 slower than Web2?
For reads, no — an RPC call takes ~100ms. For writes, yes — a transaction takes 12 seconds (Ethereum) to confirm. Layer-2 solutions reduce this to ~1 second. Never pretend a dApp is instant — show confirmation progress in the UI.
Originally published on Ayodhyyya. Last updated June 1, 2026.