Understand that the goal of the game is to draw the most squares.
Step2
Draw a square or rectangular grid of dots evenly spaced apart, or simply grab a page of graph paper--although technically this makes the game Boxes and not Dots and Boxes.
Step3
The first player connects two dots (or traces the existing graph lines) with either a horizontal or vertical line.
Step4
The other player(s) do the same. Their lines may touch other players' lines, but they don't have to do so.
Step5
When a player draws the fourth line to complete a square, he claims the square and writes the first letter of his name inside it.
Step6
Once all of the possible horizontal and vertical lines in the grid have been drawn, count the number of squares for each player.
Step7
The player with the most squares wins.
Tips & Warnings
You can alter the rules slightly to allow a player who completes a square to immediately take another turn. She keeps going until she draws a line that doesn't complete a square. You can even have rules that allow the player to choose whether or not she wants to continue after completing a square.
Another, more complicated option is to allow players to earn points by completing larger squares; for example, eight lines (2 x 2 squares) or 12 lines (3 x 3 squares) instead of four.