You just complete levels!

For completing a level you can get from 1 to 3 stars, depending on the number of points you get.

Matching tiles faster helps get more points as it increases the multiplier (you can see it at the end of the points bar which is located at the top of your game screen). The multiplier multiplies the number of points you get by the number in the multiplier. Also, the bigger the multiplier, the more bubbles you get at the end of the level.