There are very nice tutorials available for learning opengl-es you can learn them here :
- You can check this learning opengl-es ios
- There is a nice video tutorial by Brad Larson here : opengl-es video tutorial
You can read these tutorial by Ray Wenderlich here : Opengl-es tutorial ios
There is a nice tutorial series here : ios opengl-es lessons
check a great opengl-es tutorial series here.
Hope it helps you.