Green Baize Groovers (snooker/pool) is a hard game that will give you a huge challenge when you start playing against the computer, because it is too skilled for the majority of the players. However, such a game will teach you how to position your balls in order to have a continuous flow at the table.
If you happen to miss a shot, the computer will pot every other ball on the table in a single break and you will lose the game, so if you want a more relaxed gameplay you can start a game against a friend, over the Internet or from the same computer.