Oof, sorry to hear that guy was giving you a hard time. D: Still, I'm glad you're back! And good luck; high school can be challenging, but it's also a rite of passage into adulthood. It's a very exciting time of life!
Depends on how you've set up the document. I have my program set up so that it automatically opens up as a transparent document, but if you have it set up so that it defaults with a white background, turn the background layer into a normal layer by double-clicking it, then delete it.