How do you get the stars, to unlock the buildings?

As you play new scenes, you fill stars, which are totaled on your main screen. Each mastered scene gives you 5 stars (25 stars per chapter). They are markers of your game progress and do not decrease in number. As more stars accumulate, more items become available in the store and (in conjunction with compasses) more land can be opened. Make sure you master all scenes to get all the stars.