You should really check out
OpenGL.org and read what is called 'the red book' and the 'blue book'. If you've read these, you're an OpenGL guru... they're quite tough though as I've been told, but there are tutorials on the site as well.
One of the best ways to learn is to study the NeHe-tutorials
on Nehe Productions. They're available in almost any language, but the meat of the code is OpenGL itself, which is sort of language independent.
You should also now some vector-math, and have a general knowledge about 3D graphics (things like polygons, vertice, shading algorithms). If you're new to the whole thing start by doing this tutorial:
Vector Math Tutorials for 3D Computer Graphics!
OpenGL is hefty stuff, but extremely powerfull! Use it wisely and stay away from the Dark Side (Direct3D, that is)!