I know nothing about extentions. What they are doing? At the moment I believe the include special functions for some hardware. Right?
How do I use them?
What are the dis/advanteges?

They are extending OpenGL’s capabilities.
Advantages: New fatures.
Disadvantages: the end users hardware does not necessarely support the specified extension.

You need to find out an alternate way to do the effect you wanted.

You can get more info on them on sgi’s site (http://oss.sgi.com/projects/ogl-sample/registry/) or nvidia’s developer pages (www.nvidia.com/developer).