Any beginning book (or online tutorial) on servlets and JSPs will help with this. Google for "more servlets pdf" and "core servlets pdf", you will find two dated but still usable books available for free online. The "more servlets" book has a pretty good chapter on web.xml, and the earlier chapter on servlets will tell you all you need to know for your web.xml file.
Thanks a lot.
I have got the page about servlets. This page include much more information that I need but, in fact, I think all the information will come very well.