someone please explain an orgasm

I've never been someone who was comfortable talking about sex so when we didn't really cover it in health class at school I didn't mind, but now that I graduated I'm like what the hell? the last time I had any sex education was in the eighth grade and the whole lesson was more or less "don't put on two condoms" I don't even really know what an orgasm is or how to have one. does orgasm=cuming ? does it just happen? will you KNOW when it happens? every time my mans doing his thing down there with his hands, I feel like I'm going to pee, is that what it feels like when you're about to have an orgasm? is squirting the same thing as an orgasm? I feel like I don't know what is supposed to be going on down there