As soon as you gain control of Mario, the game starts you off on a 2D level. The Toads will tell you small tips on Star Bits and Jumping. Proceed onto the next screen to gain a new ability. After you get the spinning ability, you can now break crystals! You may wish to practice collecting Star Bits, but they still don't go to your overall total later on in the game. Then, a Luma encased in a crystal will fall down. Spin the crystal to free him. Head into Toad Town.
In this next area, Bowser has already seized control and kidnapped Peach. Head up front to confront Bowser, but he'll fly away. Head over to the Peach's Castle Bridge to make the Luma TRANSFORM! Use the Launch Star to fly into the first galaxy.