0x38ed1739?0x38ed1739 is the function selector for swapExactTokensForTokens(uint256,uint256,address[],address,uint256). Swaps an exact amount of tokens for another token.
When a transaction's data begins with 0x38ed1739, it is calling swapExactTokensForTokens. The selector is the first four bytes of the keccak-256 hash of the signature swapExactTokensForTokens(uint256,uint256,address[],address,uint256), which is how wallets and explorers work out which function a payload is for.