The goal of the School mini-game is to separate all the colors in different test tubes before time runs out.
You can select test tubes by tapping on them. Colors can only be poured in either empty test tubes or test tubes that both have the same color on top. You cannot pour colors into full test tubes. You can tap the "Undo" button to undo the previous move you made.
If you run out of time, you can pay Diamonds for extra time. Or you can exit the game and try again.