This is a ping pong game where you also have to avoid enemy attacks. Move quickly and intercept the ball, without getting hit by the various weapons which your enemy launches at you.
You control the bar on the right; use the up and down arrow keys to move. Press the 'J' key to activate the weapons which appear in the squares at the bottom of the game. Try to make the ball bounce off your bar, and avoid enemy attacks, or your energy will be depleted and you'll lose.