Intro:
Before you begin
Step 1:
Learn the fuseki
Step 2:
Learn to make groups
Step 3:
Learn to capture
Step 4:
Avoiding the ladder
Step 5:
Avoiding suicide
Step 6:
Using eyes
Step 7:
The ko rule
Step 8:
Ending and scoring the game

2torial #0589:
Learn2 Play Go (continued)

The ko rule 

In go, it's possible for players to create situations that can be repeated indefinetly. Here's an example:

A. In the first graph, X marks a point where black can play and capture white to the left of it.

B. In the second graph, you see the results of that move, with another X where white can play to capture black on its right.

C. Now black can capture white, repeating the whole process.

You get the picture--the moves could go on for quite a while. Luckily, this is forbidden by the ko rule. According to the rule, you can create a ko situation, but you can't immediately recapture. You can, however, try to lure your opponent away to play in another area of the board--a strategy called a ko threat. Once you both make moves in another area, you allowed to return to the ko situation and recapture (and then it's your opponent's turn to employ the threat).