When you click the green flag, there will be a cannon and that cannon will follow your mouse-pointer. The cannon is also draggable. When you click anywhere on the screen or press the space-bar, a ball will be fired. You can chose the force of the ball by how close your mouse is to the cannon. It is very fun to see what happens!
Thanks to @griffpatch for the tutorial on YouTube. It helped me make this game! So thanks @griffpatch If you would like to see the tutorial for yourself, click this link. https://www.youtube.com/watch?v=Ge1DbXkyMKo