glFrustum()

Can someone please give me a short example of the glFrustum function, especially in relation to moving the near and far clipping planes. I have tried using it, but I keep getting rather strange looking objects floating around in my world, ack! I think it is just because I don''t really understand how the function works other than what they said on an OpenGL website. Also if you could tell me whether or not to parameters in the function are in pixels, world units, or some other unit of measurement, that would be very useful. Any help would be greatly appreciated!