Are you a dude? If you are a dude, and fluid comes out that's not pee, that's cum. Ejaculate if you want to get technical. If you are a girl, the "big O" is different for every woman. For some it's like a sneeze...down there. For others it's a series of muscle spasms...down there. Could be a tremendous build up of emotion, and then a tremendous sense of relief. Could be a combination of all of those. Not to be rude, but I suggest you masturbate. You need to know your own body, alone, before anyone else can know your body. Once you are comfortable getting yourself there, you will be more comfortable letting other people get you there. That way you will know if you've had one. Good luck! :0)