mark-it's the tab that says friends under the PLAY NOW button on the left. Click on it-if nothing is there it's because you don't have any friends yet. You need to request them from whoever you want on your friends list. When they accept their name will show up in your list.
I just sent you a friend request so you can see how it works. You can ask for a friend off any profile page which you can get to by clicking the name (like off a forum post.)
YJ