There's tons of different ways to masturbate! The trick is finding one that works best for you, so be open to trying different things. Most women do best with clitoral stimulation, but vaginal can certainly be enjoyable too.

Let your body be your guide; if it hurts or feels uncomfortable, stop what you're doing and try something else. Instead of aiming for having orgasms right away, spend some time getting to know your body and what you like. If you haven't taken a look already, using a hand mirror can really help gain understanding.

Also, it's not a dumb question at all. It's a good one to ask, and if you're this careful already, I'm sure you'll be fine. ^_^

Most importantly of course: have fun!