Use up and down arrows to move the paddle on the right side. Press w and s to move the left paddle. Press "o" when you want to start. Hit the ball into your opponent's side to win. Press "space" to switch between any three of the backdrops. Press "I" to change the colour of the ball. You can slide the difficulty which will adjust the speed of the ball. This game actually got more detailed than I thought it would, so if you have any more questions, ask them in the comments. This does NOT work on mobile anymore. No, but seriously I might even make an FAQ.
Ok, now that I made a two player variant - Wait? What's that you say? You don't know what two-player is? You know. It's a game you can play with a friend. You DO have friends, right? Lol.