You were given a LOT of online references. Your teacher will also have given you references. XML is really trivial, if you can't understand it at all, then perhaps programming is too hard for you. More likely, you just need to get a decent tutorial and stick with it until you understand it. I can't give you any more info than was given on that thread, there's no magic bullet, you need to work through the tutorials you have until you understand them. If you're this lost, really your best bet is to ask your teacher for one on one help, rather than random strangers on the web.
Driven to the arms of OSX by Vista.
Read my blog to find out how I've worked around bugs in Microsoft tools and frameworks.