You can play pool in bars in San Andreas. They are dotted all over the state, but there is one on Grove Street in Ganton. Inside, challenge the person holding a pool cue to a game, and play. I won’t go into detail about how to play, but you must pocket all of either the striped / solid balls before your opponent, then pocket the black 8-ball. It’s not too difficult, and you can try again immediately if you fail. You need at least $50 to bet on the outcome of the game to play.
The video below shows you the location of a bar for, as well as how to unlock the following achievement.