FYI this is using Photoshop CS5, but every version of PS I’ve ever used has had them (Since version 4. Not CS4, 4.). Lots of drawing programs have mask functions, though, so the principles will be the same.
I try not to dwell on things that can’t be changed but if I could tell my teenage self anything about the future, it’d be these things:
Things that make marks– I love them! They’re beautiful. Today I’m pleased to own fluorescent and metallic color pencils, and that mound of Pilot Hi-Tec Cs, and flourescent gouache, and ink, etc.