General OpenGL

From OpenGL.org

This section explains the basics of the OpenGL API and answers some of the most frequently asked questions about it.

FAQ 
frequently asked questions
Viewing and Transformations 
Answers about Transformations.
Clipping, Culling, and Visibility Testing
Color
Depth Buffer
Texture Mapping
Drawing Lines over Polygons 
Using glPolygonOffset.
Rasterization and Operations on the Framebuffer
Alpha Blending 
Transparency and Translucency.
Display Lists and Vertex Arrays
Fonts
Lights and Shadows
Curves and Surfaces
Selection mechanism
VBO
NPOT Textures
Multitexture with GLSL
Vertex Transformation
GL error codes
Debugging Tools
Common Mistakes
Personal tools