Players take turns placing a stone on an empty intersection. Stones never move.
Liberties are the empty points right next to a group (up, down, left, right). Stones next to each other in a line form one group and share liberties; stones touching only diagonally are not connected.
Capture: fill a group's last liberty and it's removed. A group with one liberty left is in atari.
No suicide: you can't play where your stone would have no liberties, unless that move captures.
Ko: if you just captured one stone, your opponent can't immediately recapture in a way that repeats the board. They must play elsewhere first.
End: when both players pass in a row. The coach marks the dead stones (click a group if you disagree), then counts: your score is your stones plus the empty points only you surround. This is Chinese (area) counting. White gets komi for moving second.
A group is safe forever if it has two separate eyes (enclosed empty points). The opponent can't fill both, because playing into either one alone would be suicide.
A group with only one eye, or none, can eventually be surrounded and captured.
Turn on Territory to see which groups the coach thinks are dead. They get a small square.
←/→ step · Home/End start/latest (on the board or its buttons) · U take back · H hint · O their idea · P pass · Esc clear markers
L liberties · A atari · T territory · V preview · G grades · B best moves · N numbers
Tab to the board, then ↑↓←→ move · Enter play · PgUp/PgDn step · S speech · R repeat
The letter keys can be turned off in Settings (Single-key shortcuts).