How to use extensions?

How do i use specific extensions? Does anyone have a good tutorial? Is it like basically replacing a normal openGL call with an extension? eg:

Hey, rather than one of us re-writing all the documentation out there for you, here’s a couple good places for you to start learning about OpenGL extensions. I’m just learning about them too, and have found these very helpful.

And check out this Extension loading library, this guy has some good info:
I’ve used the extgl lib to get 1.2/1.3 functionality working in my code, as well as multitexturing.

Hope that helps!

[This message has been edited by yakuza (edited 02-12-2002).]