XML

I have three questions about XML.

1) What is it?

2) How is it used?

3) How do I incorperate it into my game?

http://www.xml.com
http://www.xml.org
http://www.w3.org/XML/
http://www.ucc.ie/xml/
http://www.w3schools.com/xml/default.asp
http://www.blitzbasic.com/codearcs/codearcs.php?code=361
http://www.blitzbasic.com/Community/posts.php?topic=38482 (see levels.bb)

thanks....