How come my jaw cracks when i open it and close it!!!!?!

You have a TMJ (aka TMD) problem and the sounds you hear is from a structure called the articular disk dislocating whenever your teeth come together and going back into place when you open your mouth. Without treatment, this will progress to intermittent locking of your jaws over time; your jaw will feel like it gets "stuck" when you open and the disk will either hop back into place on its own or you will need to maneuver your jaw around until the disk goes back into joint before you can open wide. When the disk becomes forced out of place it acts like a doorstop to prevent the lower jaw from opening wider than 3 fingers wide. You need to find a dentist who knows how to treat TMJ (not all do) but avoid oral surgeons and traditional orthodontists, trust me. TMJ is not something that you can treat yourself because it involves wearing a special appliance that must be specially made for your mouth. Do not buy a mouthguard and try to treat yourself because that will almost certainly make your condition worse and possibly cause your jaw to become locked out. In the meantime, do not chew gum and avoid all foods that require a lot of chewing like tough meats and salads.

functional orthodontist; treated TMJ since 1984

You most likely have a fractured or possibly sprained jaw. There's not really any way to know for sure unless you go to a doctor. Also try to remember if you hit your mouth on anything lately if so it's probably one of the two.