the mushroom/ring room in two ways. one is where you need to enter the ring in-order to get the bullet that allowed you to jump, so you learn how the mechanic works in a save environment. secondly you can split up the mechanics into different levels, one level for the mushrooms, and another for the rings, and then finish it off with a room that uses both of them.
i hope this has been helpful and if you are at all confused, please let me know. 