Pong is one of the first video games ever made, and it is still fun decades later. Two paddles, one ball and a simple goal: do not let the ball get past you.
When the game loads, the start screen shows the keys for both players. Press 1 on your keyboard to play alone against the computer, or 2 to play against a friend. Move your paddle up and down to hit the ball back across the green field. Every time the ball gets past a paddle, the other player scores a point.