The mask slides toward the direction which your iPhone tilts to. 
So you can control the mask by tilting your iPhone.
What you need to do is to blue and red small balls one by one with the mask.
The ball hit with the mask will disapper. Then you will get one score.
Your goal is to clean all of the 72 balls within 60 seconds.
After this game, you will get total score which is calcurated by multiplying the score and the remaining time.
The more quickly you clean the balls up, the more total scores you get.
But whenever you let the mask hit any edges of the screen, you will lose one score.
So be sure not to let the mask go toward each edge.