This is a great place to learn, I like to learn in little projects, try making a displaced cave, or a room full of interesting lights, you end up almost subconsciously picking up a tonne of information that way.
[ame="http://forums.tf2maps.net/showthread.php?t=807"]A New Mappers Best Friend[/ame]
EDIT: Oh, it's just what TPG said, again.
