Let's Learn Riichi Mahjong!

Riichi (Japanese) Mahjong is a 4-player turn-based strategy game enjoyed by amateurs and professionals alike. Each player is dealt 13 tiles, and whoever makes the first valid hand ("yaku" - usually 3 runs plus a pair) wins the round. This is the best introduction video I found:
https://youtu.be/PpgcQ3A3PVE

If you win the round, you score points. If another player wins the round, you lose points. Bonus tiles and extra yaku score more points. If a player's score becomes negative, the game ends prematurely.

All of the following are valid simple yaku:
1. Three winds matching the round (East or South) or your seat position, or three dragons
2. Declare "1-away" without assistance (riichi)
3. All sequences (3-4-5 etc.) with some exceptions (pinfu)
4. All terminals (all tiles are 1s and 9s)
5. All simple tiles (no 1s or 9s)

... however, there are many advanced rule sets and if something sounds interesting, it's probably a rule:
* 1-9 in a single suit? Valid.
* Duplicate sequence in same suit? Valid.
* All green tiles? Valid.
* Seven pairs? Valid.
* Thirteen orphans? Sure, why not.

Player actions consist of:
* On your turn, meld the tile the player on your left just discarded, to form a run e.g., 4-5-6 of the same suit (chii)
* On your turn, instead of chii, draw a tile from the deck, and discard a tile
* After anyone's turn, meld the tile any player just discarded, to form a triple (pon) or quad (kan) of the same tile (note: you can "kan" your own draw; since a quad melds 4 tiles, you draw another tile)
* Declare "1-away" (riichi) and let the game play itself until you win

Aavygeil patiently attempts to teach me how to play, while I brashly "wing it":
https://youtu.be/a-v89ebz_yU

Welcome to https://lichess.org/team/riichi-mahjong-addicts ! Now you too can be confused by amateur and professional Japanese Mahjong players alike.
Howdy, Rosy! - Table Manners

Photo Credit: Mick Haupt