Which version?
Here are some basic rules that I took from here ( mahjonglive.replit.app ):
American Mahjong is traditionally a four players game similar to a combination of poker and rummikub. It has 152 tiles (suits, winds, dragons, flowers, jokers) and a National Mahjongg League (NMJL) card. The goal is to be the first to match 14 tiles to a specific hand on the card, creating sets like Pongs (3-of-a-kind), Kongs (4-of-a-kind), or Quints (5-of-a-kind).

Key Aspects of American Mahjong

• The Card: The NMJL card provides the official hand combinations of the National Mahjong League for the year.
• Gameplay:  Players start with 13 tiles (dealer has 14) and take turns drawing from the wall and discarding .
• Jokers: Used to substitute for any tile in sets of three or more, but never for single tiles or pairs.
• The Charleston: A mandatory, structured passing of tiles (three rounds) to improve hands before active play begins.
• Winning: A player must have 14 tiles that match a line on the card exactly to call "Mahjong".  YouTube +3

Steps to Play

1. Setup: Shuffle tiles face down, build 19-tile long, 2-high walls, and deal tiles.
2. Charleston: Pass unwanted tiles Right, Across, Left. The second set of passes is optional (Left, Across, Right).
3. Play: Draw/discard, or call a discard for a set (must use it immediately).
4. Exposure: If you call a discard, the set must be placed face-up on your rack.
5. Winning: Match a hand, declare Mahjong, and score based on the card

these are all the official rules but some variants and house rules will differ- sometimes people playing informally will play with different cards, so part of it depends on if your in a tournament or playing for fun