The Social Tab is located at the bottom part of the game or the screen. It shows you and current list of all your friends. It is also a short cut access to your friend's account details including yours. See image below in red indicator for the Social Tab.
From the Social Tab you can also easily do the following;
- Change your nickname/account name
- Get gift from your friends
- Send gift to your friends.
If you want to know more about changing your nickname or account name refer to the link Here.