First, tap on Kiran, the astronaut sprite at the start. Wait for Kiran to talk and she'll go to another backdrop. Then tap the space button to see another sprite named Monet which will tell you the main task. Then wait for Kiran to tell you how to start. After that, follow the instructions that Kiran told you: Press the up arrow to make the colourful balloons move, then tap on the balloons to pop them and increase your score, press the down arrow to reset your score and if you want to stop it, just press the red stop button above the game. To restart the whole game, tap on Kiran and she will start the whole game again. If you restart the game by tapping on Kiran and then you want to stop it, tap on the red stop button above the game. Good luck.
