(Copyright © 2000-2001 --
this item revised 26 Nov 2000)
Before you post this query, check this FAQ for references (duh!), but also use the Web search engines like Yahoo, Altavista, and Google.
If you truly can't find anything in those resources, it's okay to post a query, mentioning where you have already searched.
But be aware that the Web is not the best way to learn most math topics. "Dead trees" still have their place: a textbook puts much more information in your field of view, and the pictures "download" a heck of a lot faster.