transfer operation.
To attach a comment, the message has to encode it in forward_payload field, and forward_ton_amount is some amount of Toncoin attached to let the receiving wallet process the message.
Format of forward_payload for comments and other kinds of attached data can be found in the API section. If forward_ton_amount is 0, forward_payload doesn’t have to comply with the schema.
A single manual transfer can be done with a web service (for example, Minter).
A programmatic transfer is usually done with an SDK (for example, assets-sdk) that handles low-level message serialization details. The provided example uses TON Center API that might require a key. Also you’ll need a mnemonic of a wallet that will pay for the transfer.