Here feel free to post your nickname that you used to sign up to GameCenter so that people can add you as friends. If you are unsure of what it is, you can find it by opening the Gamecenter app, going to the "me" tab (the leftmost one) and you will see it displayed. If you wish to add someone as a friend, go to the friends tab and tap add, and if you'd like to aproove someone's request but had missed the initial notification, go to the requests tab.
Now, to get things started, my nickname is pitermach. Feel free to add me.