You shoot, with the mouse button or space. You must shoot into the blue rectangle. On top in the middle there's a variable, that shows you, how many balls still need to come into the blue rectangle. The variable on the tank shows you how many balls you still can shoot.
Thanks to @Griffpatch for the Tutorial. Link: https://www.youtube.com/watch?v=Ge1DbXkyMKo Sometimes, it can be, that that there are bugs.
