Quick answer
The American game is played against a card of legal hands the National Mah Jongg League publishes every year, while most Chinese and Riichi winning hands share one general shape, four sets and a pair. American Mahjong also adds eight jokers and a tile-passing Charleston before play, and a discard is never called for a run.
Search 'mahjong' and you'll find solitaire tile-matching games, Chinese classical play, Japanese Riichi, and the American game with its yearly card. They use the same tiles, and each has its own rules. If you're joining a US club, here's exactly how the American game differs and which parts of your Chinese-rules experience (or that solitaire app) carry over.
The card
American Mahjong is played against a card of legal hands that the National Mah Jongg League publishes every year. Chinese and Riichi mahjong build most winning hands from one general shape, four sets plus a pair. In the American game, if your 14 tiles don't match a printed line exactly, it's not a hand.
This is why the card is replaced every April, and why each April brings a new set of hands to learn.
Jokers, flowers, and racks
American sets add eight jokers, wild cards Chinese classical play doesn't use, plus interchangeable flowers and the racks that hold and display tiles. The joker rules (no pairs, no passing, exchanges from exposures) are American rules.
The Charleston
The Charleston is the American game's pre-game passing ritual (right-across-left, optional reverse, courtesy) that lets players shape their dealt tiles before the first discard. Classical Chinese and Riichi play have no passing round, so play begins off the deal. The Charleston adds a strategic layer those games do not have.
Calling, scoring, and pace
American play restricts calls to groups of three or more for exposed hands (plus the game-winning tile), where Chinese rules allow chows (sequences) off the previous player. American scoring follows the card's printed values with doubling rules, while Riichi counts han and fu. For pace, League tournament rules allot about one hour for a round of four games.
If you already play Chinese or Riichi mahjong, you know the tiles, the draw and the discard, and calling. The card, the Charleston, and the joker rules are new skills, and the lesson track teaches each one.
Put it into practice
New to the game? Start the course at Lesson 1, Meet the Tiles. The first three lessons are free and need no account.
Already play? Have the coach read a real dealt hand for you, free. It names the direction the hand goes for, what to keep, what to pass, and the reasoning behind each call.
If you come from Chinese or Riichi mahjong, the new skill in the American game is reading a rack against the card. Mei, our AI coach, reads a hand tile by tile, names the direction it goes for, and says what to keep and what to pass, free.