how do I use extensions, do I have to download something else or no?

Depends on what platform you are coding for, but generaly, no, you don’t have to download anything, except a document or two that explains how to use the extension if you want them. Tell me whan platform you are using and maybe i can tell you how.

I am working on all platforms actually, that is except macintosh, but mainly on wnt4

In Win32 version of gl.h there are some macros defined (almost in the bottom of the file) called PFN*PROC, these macros defines a functionpointer you can use to access extensions. An example:


Then you have to check if we got a proper poiner, like this:
if(!glArrayElementPtr) exit(1)

If this passed, you can now use your extension like this:
Maybe even like a standar function too, not sure, glArrayElementPtr(i);

You have to check out your copy of gl.h to see what extensions are predefined. If you are looking for other extensions, just have alook at the extension registry ( http://oss.sgi.com/projects/ogl-sample/registry/ ) and look at the extesion you want. There you can find the exact prototype of all extension aswell as a description of them.

Using extesion under UNIX is nothing I know about, but keep on asking and you will get an answer.