Original: The ways to win a steel cage match are as followed; either pinfall, submission, or by escaping the cage (over the top or through the door) and having both feet touch the arena floor.
Simplified: A steel cage match is a match that literally takes place in a steel cage which surrounds the ring. You can win by pinfall, submission or escaping the cage by climbing over with both feet hitting the floor outside or by exiting the door with both feet hitting the floor.