You will need a sheet of squared paper or 'grid' paper. If you don't have any, just rule some lines down some lined writing paper to form squares. One hundred squares (10 by 10) makes a good size game board, but you can use a smaller of larger grid if you prefer.
Two players, using two different colours, take turns to mark a
'cross-road' on the grid.
The aim is to make a line of four, across, down or diagonally.
Each 'cross-road' can only be used once.
Try to block the other player's path.
Each time you make a line-of-four draw a line through it so it can be counted as a point.
When all the 'cross-roads' have been used, the player with the most points wins.
In the example below, each player has had 10 turns so far. The green player has already scored 2 points, and the red player has only one point.