How to play
Each player gets ten cards, and one card is turned up to start the discard pile. On your turn, take the top discard or the top card of the stock, then throw one card away. You can’t throw back the card you just took from the discards.
You’re trying to arrange your cards into melds: sets of three or four cards of the same rank (three 8s), and runs of three or more in a row in the same suit (5♥ 6♥ 7♥; aces are low). Cards that aren’t in a meld are deadwood, counted as aces 1, picture cards 10 and the rest at their number. The game sorts your hand into its best melds for you, shown in green.
Knocking and gin
When your deadwood is 10 or less after your discard, you can knock to end the hand. Your opponent shows their hand and can lay off loose cards on your melds (a fourth 8 on your three 8s, a 4♥ on your run). If your deadwood is lower, you score the difference. If theirs is the same or lower, that’s an undercut: they score the difference plus 25. With no deadwood at all you go gin: no laying off, and you score their deadwood plus 25. If the stock runs down to two cards, nobody scores. The first to the target (100 or a quick 50) wins.
Tips
Throw away high cards that aren’t helping early, since they cost the most if you’re caught. Watch what your opponent takes from the discards and don’t feed them more of it. Knock early when you can; waiting for gin is a gamble that the other player might win first.