2 players. Draw one card (from the stock, or the top of the discard pile), then discard one card to end your turn — unless you knock or go Gin instead.
A set is 3-4 cards of the same rank in different suits. A run is 3+ cards of the same suit in consecutive rank order (Ace is low only).
Deadwood is the point value of whatever cards don’t fit into a meld (face cards = 10, Ace = 1, number cards = face value). Melds are never shown to your opponent until the hand ends.
Knock when your deadwood is 10 or less to end the hand and reveal both hands.
Go Gin by knocking with exactly 0 deadwood — a bigger bonus, and your opponent gets no chance to lay off.
Go Big Gin if all 11 cards (including the one you just drew) already form complete melds — no discard needed at all.
On a plain knock (not Gin), your opponent may lay off their own spare cards onto your revealed melds before scoring.
If your deadwood ends up equal to or higher than your opponent’s after they lay off, you’ve been undercut — they score the difference plus a bonus, instead of you.
If the stock runs down to its last 2 cards with nobody knocking, the hand ends with no score for either side.