As a developer sending out free keys, I'm a bit confused as to what exactly I'd need from the other person.

Let's say User X exists outside of Steam and has an opportunity to be given a key to a game I have created. User X tells me that they do have a Steam account, and that their name is UserX.

Is this what I'd need, or is there some kind of code or special unique identifier I need to obtain in order to send them a key and they receive it?

Thanks.