Touch Screens:
This game was designed for touch screen, and as such works well with simple finger input. Tap the simple UI to move around. When starting the game, tap once the drop the ball, then tap and hold on the left or right to control the paddles.
Computers:
Mouse input works the same way as touch input, and you may also use the left and right arrow keys to control the paddles. The space bar will also navigate some menus.
Best played when downloaded on phone from Google Play.