I dropped a hammer on my foot and its swollen and bruised. how to tell it's broken?

X-ray: The best way to tell if a bone is broken is to get an x-ray. All of those other things you learned, eg if you can move it then it is not broken, are not reliable.

Radiographs: Anytime you have an injury and you suspect that you may have broken a bone, the best way is to have a specialist perform a thorough examination and a series of x-rays. They are inexpensive and an extremely valuable tool.