The game starts with 33 tiles that are shuffled out to the 4 players, 3 with 8 tiles and the first to go with 9. You try to be the first to make 3 sets of 3. A set is 3 of a color, but stuff like 3 of a kind (ex. 2, 2, and 2) or a run of three (1, 2, and 3) is worth more points.
The first person has to discard one of their 9, which the second person can then pick up. At the end of their turn, they have to discard one. Like so, tiles are passed around, till someone completes their 3 sets.
Also, when you have 2 sets complete, and only need one more tile for your last set, you have to call it out, similar to saying "Uno" when you have one card left in "Uno". At that point, If any player discards the tile you need, you can swoop in and nab it, completing your last set and ending the round.
You then steal points from whoever discarded that last piece, based on what sets you have made. The game ends when someone runs out of points.