The site you mentioned is very good, but I think the best one I have found is by INsanityDesign. It is a portof the great opengl nehe tutorials. This is a great place to start, it gives you source at different levels that you can play with and change to see what different parts do. Other than that reading opengl documentation, will help as well. I am not great at the opengl stuff, but have been able to figure things out using the resources I mentioned.