You've already seen this level before; it is the title screen level in which there is a demo of it before you begin playing the game. This is a simple level to play. There are Pokeys, which, if you have Yoshi, he can simply eat to allow you to continue on (there is a [?] Block early in the level which has a Yoshi if you don't).
A changing block also appears within the level. Hit it to receive a Starman and then continue on.