There are two opengl versions around: The original OpenGL
] and the freeglut library
The latter is more widly used actually, and of course is compatible with the original OpenGL.
From both version you can download development kits, for the freeglut there are also some other resources as this
] where you can found complete precompiled development packages and samples.
On the OpenGL site on this page
] at the tutorials section you'll find many resources to learn how to use OpenGl.