From the Super Mario Wiki
“Hey! Before you ride any bubbles, let yours truly, Phil Board, bend your ear for a sec. You can move around in your bubble by holding down A. But do it while your Star Cursor is blowing on the bubble.”
Bubble Blowing is one of the four minigames in the Wii game Super Mario Galaxy, along with Bob-omb Blasting, ray surfing, and Star Ball Rolling. In the game, Mario must jump inside a bubble. The player then must use the Star Cursor to blow Mario around. This minigame can be played in the Bubble Breeze Galaxy and the Bubble Blast Galaxy. It is played both times over a hazardous substance. It has a small part in Gold Leaf Galaxy's The Bell on the Big Tree where all the Rainbow Notes must be collected around the big tree. Unlike the other galaxies, the player cannot lose a life if he or she falls. Also, the player's ability to shoot Star Bits using the Star Cursor is restricted while participating in Bubble Blowing.