If you're serious about making maps or textures for Quake3 you will want to know about shaders. If you want to know about shaders you need three things.
The Shader Docs provide all of this.
You don't need to be a 3d guru to grasp the basics of shaders as the overview covers the essential terms and concepts. However, understanding some of the more complicated effects might require a knowledge of OpenGL and 3D graphics terms such as z-buffer and culling.
Comments in brackets with an asterix beside them (* like this *) are reminders for me. Ignore them.
Words in italics are usually defined in the Glossary.
"Computers don't make mistakes. What they do, they do on purpose."
Dale (King of the Hill)