You'll need the specific Shimano STX-CCRT-3500 crank removal tool. I don't think that its made anymore, but you might find it on EBay :-).
Seriously, its just a regular square-taper crank removal tool. Everyone uses Park, I like Sugino and Lifu more. All of 'em work. Just be sure that you thread the tool ALL the way in before applying torque to the extractor stud, otherwise the tool will pull the threads out of the crank, ruining it.
If the best way to learn bike mechanics is by making mistakes, I guarantee you will never learn as much as I have.