Who Did & 4 Who?

[Come2Daddy]

This question may seem very basic 4 some of you, howver I'm still in the basic stage. I'd like to know how the visitor's messages works, I mean in the new versions 3.7.x each user can leav a message for another user and that works as a form a user fill it with his message so which tables of the database are involved in this?? and if there is a tutorial or example 4 this 2 show how the coder identify/determine who did it & 4 who?? I'd appreciate it :$