Basically, if you don't know why you would use Terminal, you don't need to use Terminal. 🙂
Terminal is used to get at things you wouldn't normally need - making files hidden (or unhidden), seeing files the GUI doesn't show, running scripts to do things like update a DNS server with your current IP address, etc. There's pretty much an infinite number of things you can do with it, as with any Unix terminal. If you can read about Unix - as mentioned by 7on - you'll see what you can do. There are also specific books, like "Learning Unix for Mac OS X Panther", an O'Reilly book by Dave Tayor & Brian Jepson.
Note that Console is used mainly to see logs of what's been going on, and Terminal is what you want if you're going to play around.