Super Mario World/Yoshi's House

You start the game at Yoshi's House, which you can access at any time. There is no time limit in this area. If you hit the message box without Yoshi, you will get the message saying that Yoshi is not home. If you hit the box while Yoshi is with you, the message will be different. Also note the little birds on the top of the trees, they have the same colors that Yoshis have.

Clearing the level
Simply walk off the screen in either direction.

Other uses
If you have Yoshi, you can keep entering the level to eat berries, and eventually gain extra lives. You can also practice jumping in this area. There are no other uses in this level.