In the World Tour game mode, there are 24 levels split over six worlds that you can play through. The ultimate objective is to save Peach from the clutches of the evil Bowser.
As you run through each stage, the objective is to collect as many coins as possible, while avoiding the enemies or falling off the stage. If you make a mistake, you'll return inside a bubble and get to try again - tap to break open the bubble and continue playing.
The free version of the App contains the first three stages of World 1, and a 20 second preview of the 4th stage.