[left] and [right] arrow keys let you select different billiard balls.
[z] or [x] confirms your selection.
All four arrow keys are used to aim, and [z] or [x] fires the ball.
Knock all your opponent's balls into the pockets - good luck!
(P.S. the game won't know when the game is over...so when you knock all your opponents into the holes, you'll have to invent your own appropriate celebration)