You've been taught this at every drum camp you've attended. You even wrote out some just to get your mind around it. Now have an app in your hands to create the grid of your own choosing. 4-2-1 style. move the accent. move the beat. triplets or sixteenths. forwards, backwards. change the sticking. 

What can you create? What will challenge your hands? Now challenge your friends! Practice Daily. Get Better.