Hi, I have a game app based on OpenGL. I'd like to add Game Center and iAd support to my application. What is the easiest way to add these to my app. From my searches online, I figured first I need to add a viewcontroller. Is there a good tutorial to do this? Any tricks is much appreciated.

First stop: Read the documentation.
https://developer.apple.com/game-center/

There's a lot there.