Press the green flag. Press space to start the game. The paddle will follow your mouse-pointer, and you must stop the ball from touching the red laser. Sorry about the fact that you start with 2 points- there is a bug where if you start with 0 you die automatically.
Thanks to Helioscape- that's where I got the 'world high score' and 'your high score'. I used some things from the step-by-step, but some I made up.