OpenGL levels

Hello people.

I was reading these OpenGL tutorials , and it was goin' on about textures for your levels , an stuff , but it didn't say how to actually make the levels. ( For a 3D first person shooter if it matters. )

If someone could please tell me where to start , that will really give me a headstart.

Sorry if this was a stupid question.
Thanks again.

I'm not an OpenGL kind of person, but I really doubt there is a prebuilt method of saving levels. You will need to make your own. I've made some clever level saving things in a .txt before, but you will probably end up making your own extension.

EDIT
I'll try and give a more useful answer. To save a level you're going to need to find all the information which is going to be vital to recovering the level identically, and output that to a file. You could seperate each block of data with a special code or character, in addition having a header which tells some information about the stored data is also useful.

http://nehe.gamedev.net/lesson.asp?index=02 <-- Have a look at lesson 10

also, http://nehe.gamedev.net/ is a great place to learn many basic and advanced OpenGL techniques.