Hi Aditya,

thanks for the feedback. These Solidity files are part of the OpenZeppelin package and you would find them in the node_modules/@openzeppelin-solidity. Since we import these contracts in the main contract TestERC20Contract.sol you also compile those and are saved as JSON files in the build/ folder. In these JSON files you'll find the abi, the bytecode, the topics (if you have any event in your smart contract), the function definitions etc.