You start by pressing the green flag and then move the paddle (by moving your mouse)so the ball hits the paddle, every time it hits the paddle you get 1 point.
Thanks to https://www.youtube.com/watch?v=sCd14qXFdPo&t=24s for how to make it. I am not one of the people who asks for likes or something, but if you like the project just comment about what you like below.