Rereading the question, I’m not entirely clear on whether the activity being discussed is pleasuring oneself in the presence of another or pleasuring your partner with your hands. Either, however, can be a primary activity.
Consider that lesbians have no form of toy-free penetrative intercourse except fingers. Consider also that many women can’t get off without clitoral stimulation—which you don’t usually get through PIV without a little manual stimulation. Some of them enjoy oral, but some of them don’t—I’ve been with partners and talked to friends on either side of that fence. (Some people, even, don’t like sex with other people.) For a lot of these people, touching themselves or their partner is a primary form of sex, not some secondary activity they engage in on the way to “real” sex or when they can’t have sex. And if it’s a primary activity for them, it certainly can be for you as well. It sounds like most people responding right now don’t enjoy handplay as much as penetrative intercourse (though I also suspect that the perception of sex in society discourages people from exploring it too much)—obviously everyone enjoys different things—but for @Blackberry to make blanket statements such as “Masturbation is what you do when you can’t have sex,” is invalidating to everyone for whom that’s not true. Which is a not-insignificant percentage of the population.
If you’re only 13, this might all be a little heavy and intellectualizing for you, but I hope it all makes sense.
The first time I touched a partner sexually (I was probably 14 or 15?) was very awkward. We didn’t really talk about sex, so there was no sense of what was or wasn’t allowed. Retrospectively I can see that I was pushier at first than she wanted me to be. However we did end up falling after not too long into a sexual routine (consisting only of kissing and touching) that seemed to be comfortable for both of us and pleasurable as well.