XML confusion

I think I'm getting bogged down in details.
Ajith,
What is an entity reference? what is it good for? What is an entity? How are they different from an element or other node types?
Anybody have a good online reference that explains any of this clearly?

I was getting confused reading about Document objects. Most my questions were cleared up here:
http://java.sun.com/xml/jaxp-1.1/docs/tutorial/sax/5c_dtd.html

To clear up rest of your questions (and provoke new

):
XML Entities and their Applications
By: Pankaj Kamthan
Ok, Ok, here is less verbose text

:
Entities: What are They Good For?
by Norman Walsh