The friends list shows if your friends are 'Online' or 'Offline' in the game, in addition to providing various options such as private messages, Edit friend, being able to put an icon and description for your friend, and also the option to ignore the player.
To add a friend is very easy, just right-click on the list, select the add friend option, and type the name of the player you want to add as a friend.
Another way to add someone is by holding 'Ctrl' and clicking on the player you want to add, then selecting the 'Add to VIP list' option.
