The one on the left (Player 1) uses w and s. The player on the right (Player 2) uses the up and down arrow. For the bot, it will be on the left, and you will be still controlling the right one with the arrow keys. (WARNING: the bot is basically impossible to beat.) FINAL GOAL: Make it so the ball gets past the other player's paddle.
If one of the players start with 1 point, just click the green flag again, scratch is buggy some times.