The rhythm of mahjong fits one sentence: players take turns “draw one, discard one”, and the first to build 4 melds + 1 pair wins. Here's the flow in order.
Choose the dealer
Dice are cast to pick the dealer (East). The dealer acts first and starts with 14 tiles; everyone else gets 13.
Build & deal
Players stack tiles into the wall and draw starting hands — 13 tiles each (dealer: 14).
Draw & discard
On your turn: draw one tile from the wall (14 in hand), then discard one you don't need. Back to 13.
Chow / Pong / Kong
If another player's discard fits your hand, you may claim it and lay the group open as one meld.
Win
Complete “4 melds + 1 pair” and you win — by your own draw it's a self-draw win; off another player's discard, they dealt into it.
Seating and the “previous player”: why chow only works on them
Players sit 東南西北 (East, South, West, North) and play moves counter-clockwise: East (dealer) → South → West → North. Your previous player is the one to your left — tiles flow from them, through you, on to the player on your right. The rules say only your previous player's discards can be chowed, while pong and kong work on anyone's discard. That's the only thing you need to memorize about seating.
What the dealer is
The dealer (East) is simply the first player of the round: first to draw, one extra starting tile, and if they win they keep the deal. The deal rotates counter-clockwise, so every four rounds each seat has been dealer once.
Draw games
If the wall runs out with no winner, the round is a “draw game” and is redealt. Getting ready early matters — if you're still not ready when the wall thins out, the round is probably lost to you.