Use the grey ball that can be dragged with your mouse and knock the smaller balls in the holes.
Levels 1-4 •
Use spacebar to spawn a ball, if you get an extra ball don't spawn another yourself (It's reccommended to use one ball at once).
Level 5 •
With a mouse click spawn the red ball, with spacebar spawn the blue ball, you must knock the balls the holes that have their colors.
Ball Knock 2 coming up with more levels and with Level 5 features.