What components make up a light source in OpenGL?

If a coordinate system (CS1) is transformed to another coordinate system (CS2) using a matrix M, is it possible to go from CS2 to CS1 and how?

What are the valid operations provided to glStencilOp?

What does glMaterialf(...) do?

When animating, OpenGL provides:

Can you specify the location of a light source in OpenGL?

Which buffer type is supported in OpenGL?

On which matrix stack should gluOrtho2D be used?

What does gluOrtho2D do?

Purpose of glTexCoord?

How do you initialize the name stack?