2-players sit across from each other at the table.
You pull the 34 tiles in front of you after setting up the wall, then you build your 13-tile hand from those tiles so it's in tenpai (1 tile away from winning).
Then you and your opponent take turns dealing your own deaths, hoping that you don't lay down the tile that completes your opponent's hand.
It also looks like they turn over a 'Dora' indicator tile.
If after 17 discards no one wins, then it is started over again.
As for the stakes, I'm not sure, but they've got to be pretty high.