Birth control..

Ok so I don't know much about birth control but I heard it will help with cramps which I have the absolute worst you can imagine I just lay in the floor in a ball crying with my heating pad and ibuprofen doesn't work and the heating pad helps, but they're still there. So I just wanna ask... what else is birth control gonna do to me and how long do I have to be taking it for for it to actually work? And how effective is it for me not to get pregnant?