OpenGL & Cg - How does it affect each other

[N O R B E R T]

I recently found out that I don't really understand how OpenGL and Cg shaders work together. My shallow knowledge of this topic was that more or less every option set in OGL could be reset in Cg. That works for vertex positions, light positions, texture coordinates and texture IDs and a lot of other stuff. But OGL render options like drawing full faces or only grid models can't be overridden in Cg. At least I couldn't do it. I wanted to ask if anyone knows a good tutorial concerning this topic. thanks, Norbert