Dead - Introductory
This is an introduction to dead stones. Take a look at the white stones below:
It takes 3 moves for black to capture the white stones. But it would take 15 moves for white to capture the black stones, and the white stones have no way of escaping. In go terminology we say the white stones are dead. Even though they are still on the board, black can capture them at any time. It's usually a bad move for black to capture them right away: because they can't escape, both players will usually leave the stones until the very end of the game.
Now consider a shape like this: are these white stones dead? They can't escape. But black can't play the point inside, it's suicide.
This shape is called an eye. But one eye is not enough. Black can fill the outside points first:
Now what happens when black plays that inside stone? The white group dies, because it has no liberties left. The rule is: Always check if your move captures BEFORE you check if it is suicide. So the white group is still dead. As in the last case, usually neither player will play inside that space until the very end of the game (or after the game ends they will be removed by agreement).
This shape is also dead. This is called a 2-point eye, because there are two points inside instead of just 1 as in the above diagram. First observe that white doesn't want to play inside: it creates the 1 point eye, which is dead. What if black plays inside?