X-ray
An X-ray uses a small dose of ionising radiation. It takes seconds. It is excellent for fractures, some chest problems and checking the position of a joint. It does not show cartilage, a disc, or most brain detail.
MRI
MRI uses no ionising radiation. It takes 15–60 minutes and shows muscle, ligaments, discs, brain and many organs. It is a poor way to answer “is it broken?” when an X-ray already can.
A common path
Joint injuries often start with an X-ray to exclude a fracture. MRI follows if pain continues and the question has moved to cartilage or ligament. You do not need both for every problem. You need the one that matches the question.