In the Microsoft Sudoku game, players use simple logic to fill in the 9 rows and 9 columns of the puzzle with numbers 1-9. Each number can only be used once in a given row or column. Enter the correct number in each grid square to win! Sudoku has two modes, pen and pencil. In the game, players can click the pen button, then click the left mouse button on the square and drag the cursor up and down to enter the "pen" answer. You can also enter numbers. If you are unsure of the answer, you can choose the pencil button. Hover your mouse over a square and click the number you want to enter.