1 Player: Up- and down-arrow keys move your paddle (the left one) up and down. The opponent's AI is set to 5 as a default. It can be adjusted using the slide bar. Higher difficulties give the opponent a quicker reaction time. 2 Player: Switch to two-player mode by clicking the button in the top right corner. The second player controls the right-side paddle by use of the 'w' and 's' keys. Those little blue circles that keep popping up will randomly change the direction of the ball if it passes over it. They appear and disappear at 10-second intervals.
So far, there's no score. Just have fun, try to resist yelling at me, etc.