When you are playing a game there is a little heart above it, if you click it the game will be added to your favs. To add someone as a friend you have to click in the "Add friend" button in the top right corner of their profile. It's recommended for you to ask the user if it is alright to add him before doing so.
P.S.: Please try to be a little bit more polite when asking a question in the forums.
