How do you know when a girl is cumming?

I am 17 and haven't really been in the dating scene. I read over some thingsbut it didn't really help me. I personally don't like touching myself but I do enjoy a good session in the shower. I lay down on my back and hold it in the right spot as long as possible. the better it feels my back starts arching and i twitch all over and once it feels like I can't take any more I take away the shower head. After that I feel pretty good and my area feels very sencitive. I feel very relaxed and don't want to continue any more. Is that like an orgasm or something? Or did I *** or what?