I'd suggest reading the XML specs, and learn to read DTDs.

Yes, you can use XML without understanding its intricacies, but there's no real substitute for actually knowing what you're working with.

Everyone has their own favorite XML modules in CPAN ... search on 'XML' in the Super Search, and you'll find lots of recommendations. Without knowing the intricacies of what you're trying to parse and/or create, I'd be doing a disserve to suggest any particular one.