Non-Mathematical Explanation of Go

Go is a game played on a 19 by 19 grid. Two players alternate placing black and white pieces on the empty intersections. Pieces do not move once placed, except to be removed from the board in a process called lifting. A group of pieces is lifted if, considered as a group, it borders no empty spaces. These pieces are then removed from the board as prisoners to count against their original owner in the final scoring. In the example board below, all the black pieces should be lifted.

In an actual game you would never encounter a configuration like the above, with multiple groups of pieces that should be lifted, because after every piece played lifts are determined. Consider the two boards below, then. In the first, white is about to make a move, in the second white has made the move.

White played where it did in order to lift black's circle of eight. By our current definition of lifting, all nine middle pieces, black and white should be lifted. Instead there is a different rule, which says that when player $A$ places you first consider if any of player $B$ 's pieces are lifted, lift them if need be, and then check for player $A$ 's. So in this case only the black eight are lifted, giving a board that looks like:

To ensure that the game has an end, there is an additional rule that prohibits making a move that would result, after lifts, in a board configuration that is identical to any previous configuration. This is usually referred to as the coe rule, after the coe shape.¹

The game ends when both players agree it is over, at which point they decide who surrounded what territory and agree on scores.