Shadowing

Could someone please explain to me how shadowing works in OpenGL, could you not direct me to a tutorial, because I have read a few of them and none of them really explain what is going on very well.

Thanks

prolly not useful information but shadows are quite difficult to do in opengl theres no command glEnable(GL_SHADOWS) i know of at least 4 diffierent ways of doing them all of them are quite hard. i suggest taking a look at nvidia developer website + have a search on this site