game over...  

This is an example of the end of a first 5x5 game between two players that did not fully understand the rules, but kept adding stones until the very end rather than passing in time. It is a situation that should be avoided. Can you see what it is? B and W have both filled up all their liberties, and end up without any. Stones should always have liberties at the end of a move.

White should not play !  

Let's assume White's last move - in fact the last move of the game - was . That was an invalid move, as White put herself in atari, so that move should not have been played, right? White should have passed.

But notice that Black is also without any liberties. Now let's go one move further back and look at what Black did wrong.

Black should also be careful  

Let's assume Black played . That was invalid too, as he left his group without any liberty. In fact, Black should have passed. But at that point, there's a far better move for Black, can you see it?

Black has a far better move!  

Instead, Black can kill the white group by taking its last liberty. White will not be able to recover from this loss. Because both players will continue to add stones, for each white stone will be followed by a black one and White will never be able to even equalize the stone score.

: White's mistake  

White could have foreseen the catastrophy in the previous diagram: so let's go back a move. Let's assume White played , a tactical mistake that presents the white group on a plate for Black to kill at the remaining free liberty, as we saw before. Better for White is not playing , e.g. by passing. Then, Black will never be able to kill at , as explained in the previous diagram. But White has a far better move: instead of passing...

: White's winning move  

White takes the last liberty off Black's group, and now it is Black that would lose the game. So Black should have been more careful. Let's go back one more move.

: Black's mistake  

Let's assume Black played - we saw that this was a tactical mistake of Black, better was to leave that spot open. And notice that Black cannot attack White...

The end of the game  

So Black should pass instead. White will also pass, and the game ends normally. Just remember: a group with only one liberty can be killed.

A mistake by Black...  

Let's assume that B, instead of playing 'a' (leading to the previous diagram) plays . In the previous diagram, White passed. But now, White sees a new opportunity.

... that will help White  

White sacrifies a stone...

Game over!  

Black captures the stone ... and is left with 1 liberty. Rings a bell? Welcome to Go!