Composability in smart contracts refers to the ability to combine elements from different contracts to create new, complex applications, akin to assembling Lego blocks. This concept is pivotal in the Web3 ecosystem, enabling innovations like decentralized games, NFTs, and DeFi platforms by allowing smart contracts to interact and build upon one another. The tutorial explores using composability with Circle's USDC, a stablecoin backed 1:1 by the US dollar and operating on the ERC-20 standard, which ensures interoperability on blockchains like Ethereum. By guiding users through creating a smart contract that interacts with the USDC contract to check wallet balances, the tutorial demonstrates composability in a practical context. This feature facilitates the development of decentralized applications by leveraging existing smart contracts, as illustrated by the example of Credix, which uses USDC and composable contracts for cross-border institutional lending. The document emphasizes that composability reduces the need for central intermediaries, enhancing the decentralized nature of blockchain applications.