There are a bunch of tutorials online at http://www.wrigleyvideo.com/
that are really good. The guy describes exactly what he is doing and why. I've found that I can easily duplicate the results he gets. If you start off with the simple tutorials you should be able to edit simple video clips in just a few hours (meaning it won't take you weeks to figure out the program).
Since you're in high school make sure you buy the student package so you save a few hundred dollars.