It’s really hard to answer general “how do I do this” type questions. You’ll have much better luck if you break your problem down into smaller steps and take those steps on one at a time. For example, can you create a sketch that shows a single hard-coded rectangle that “shoots” circles when you click?
If you get stuck on that, then you can post a MCVE along with a more specific question. Good luck!
You might also read this for some tips on asking questions: