In Web3, you can use smart contracts by interacting with them through decentralized applications (DApps) that are built on blockchain platforms such as Ethereum. Smart contracts are self-executing contracts with the terms of the agreement directly written into code. To use smart contracts in Web3, you can deploy your own smart contracts or interact with existing ones using your Web3 wallet and tools like MetaMask. These smart contracts can be used for various purposes such as decentralized finance (DeFi), non-fungible tokens (NFTs), decentralized exchanges (DEXs), and more.