How to Capture in Go
The go problems on this site are about capturing the opponent’s stones. Once you understand how capture works — filling a group’s liberties — you can start solving right away. New to go? Begin here.
The empty points directly next to a stone — up, down, left, right — are its “liberties.” A stone in the open has four (the green dots). Diagonals do not count.
When a stone has only one liberty left it is in “atari” — one move from being captured. This white stone’s only liberty is the point below it.
Play on the last liberty and the opponent’s stone has zero liberties — it is captured and lifted off the board (the ✗ white stone). Tsumego on this site asks you to capture the marked stones exactly this way.
Same-colour stones that touch orthogonally form one group and share their liberties. To capture a group you must fill all of them (this two-stone group has six).