To add friends, you simply click on their username to enter their profile. Then, there's a button on the upper-right side that says "ADD FRIEND" in a green font. Once you click on that, the username will become your friend, and the username will appear in your friends list on your profile.
If you cannot find their username, but know the name of the profile, then:
http://armorgames.com/user/###########
and just fill those symbols in with the name. Once you copy/paste that into your URL, the profile should pop up.
