Gonna copy-paste an old ass Mahjong guide I wrote some months back for friends so you can read this and start playing instead of having to spend hours learning the rules. I recommend Mahjong Soul for a game client.

Mahjong is a 4-player game where each player is dealt a hand of 13 tiles. When it's a player's turn, they draw 1 tile and then have to discard 1 (with the choice to discard the tile they just drew included). The victory condition for each round is to have a winning hand (a.k.a. a specific combination of tiles that let you win) before the other players. Or at least the best hand before the tiles that can be drawn for that round run out.

As players discard their tiles, other players can pick it up (and it has to be the last one that was discarded specifically) should it complete a triplet (3 of the same tile) or a sequence (3 tiles of the same suit you count up, 1-2-3, 6-7-8, etc.) Note that tiles to complete a sequence can only be picked up if it's from a player to your left. Also more important to note that if you pick up a discarded tile to complete a triplet or a sequence, you have to put those three tiles out in the open to your right side. It skips to your turn if you do this and you have to discard one tile in trade after. Taking tiles from other players creates an open hand, a.k.a., part of your hand that you reveal to other players

Open hands dictate what kind of winning hands you're able to afford for that round. All winning hands are valid if your hand is fully closed. Some are invalid if you have an open hand, at the cost of being easier to form others since you're using discarded tiles to help reach victory faster

Generally speaking the harder a winning hand is to get, and the more conditions you meet to get it, the more points you accrue if you win a round. You don't have to memorize all the combinations. Just have a chart on hand and know which yaku (winning hands) are easiest to get

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