When you load up, click on the words to change their state. If AI is on, then only one person can play. The difficulty just adjusts ball speed and paddle speed. Once your settings are configured, press space to start. For player 1, use up and down arrows to move your paddle. For player 2, use w and d. The goal is to prevent the ball from passing your paddle. Note: The AI is incredibly hard to beat, but it is possible.
I haven't shared a project in a while. I actually finished this project in early August, but just now got around to "prettying" it up.
