One player chooses an X as their symbol and the other player will have Os as theirs. Click in the square where you want to add your symbol and it will appear.
For keyboard navigation, press the "s" key to enable it. Then use the arrow keys to highlight the square you want, then press the Enter/Return key to add your symbol in that square.
The first player to get 3 X's or O's in a row (across, down or diagonally) wins!