Shape of the board
The Hex board is composed of hexagons, arranged in an n × n rhombus, where n is an integer greater than zero. Thus Hex can be played on boards of different sizes. Currently, 11x11, 13x13 and 19x19 are the most common boards. See the article Board size for more.
Here is an example of a very small board:
Playing the game
Hex is played by two players, who take turns placing pieces on the board. The players have different colours, say red and blue. The four edges of the board are coloured with the same colours, in such a way that parallel edges have the same colour. Red wins if he can build a continuous chain between the two red edges, and Blue wins if he can build such a chain between the blue edges.
Here is an example of a win by Red:
The swap rule
The above rules give a strong advantage to the first player. Because of this, the swap rule was introduced. The swap rule is also called the "Pie rule", since it resembles the You cut, I choose rule when sharing a pie between two children. Suppose that Red is to make the first move. Then the first player places a red piece on the board, in any cell he likes. After that, the second player decides who will play as red and who will play as blue. Then whoever was decided to be blue makes the next move, and the game continues normally.
Beyond the rules
For more information on how best to utilize the rules, see Strategy.