Do you want to just write an XML file or read XML using a particular language?
XSL is used to translate XML into XHTML.
These tutorials form w3schools.com might help.
I have a tutorial on using XML and the ASP.NET repeater control here
A while ago I wrote a blog in XSLT and XML http://www.whatisreal.com/index.aspx
You can view my source using the links to the right. That should get you started.