ERC-20 defines `totalSupply`, `balanceOf`, `transfer`, `approve`, `allowance` and `transferFrom`, plus `Transfer` and `Approval` events. Decimals are cosmetic: values are always integers.
function transferFrom(address f, address t, uint256 v) external returns (bool);
Watch out for non-standard tokens that return no boolean, fee-on-transfer tokens where the received amount is smaller than requested, and the classic approve front-running race (use increase/decrease or permit).