Smart contracts are computer programs that operate on blockchains, allowing them to function without a central server while being commonly written in Solidity for the Ethereum blockchain and other EVM-compatible blockchains. These contracts can interact with other deployed contracts for various purposes such as token issuance, decentralized exchanges, and utilizing services like Chainlink for data feeds or random number generation. The text illustrates the necessity of calling functions from other smart contracts, especially when an application needs to be divided into smaller contracts due to size constraints or for creating upgradeable contracts through proxies. A practical example is provided with two smart contracts—Counter and CounterCaller—demonstrating the process of writing, compiling, deploying, and interconnecting them using Solidity and the Remix IDE. This serves as a foundational exercise for understanding how to delegate calls between contracts, promoting reusability, and designing complex decentralized applications, while also suggesting the use of Chainlink for enhancing smart contract security and functionality.