You can search for their name using the member search, which you can find at the top of the screen as a drop down option when you mouse over "what's new". Click on that, and then search for the member you are looking or, and click on them to go to their profile. Once you are at their profile, there are 3 options at the top right of their profile page; Private message, Public message, and Add friend. Click on 'add friend', and if they accept your request, then they will be added to your friends list :)
