A puzzle is a 9×9 grid made up of 3×3 regions. Initially, some cells already contain a number. These numbers are called givens.
The aim of Sudoku is to fill in the partially-completed grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once.
To begin a single-player game:
On the difficulty menu, the Custom option allows a puzzle to be entered by hand (e.g. from a newspaper), rather than using a system-generated puzzle. Further instructions are displayed if this option is chosen.
To be the host of a competition:
To join a competition for which there is already a host:
The same puzzle is given to both players in a competition. The aim is to be the first player to complete the puzzle.
Each player can see their position relative to their opponent’s. There is an interesting twist, however: a player is informed, by the colour of the progress bar, whether their opponent has made any errors!
Clicking the left mouse button on a cell selects that cell, and the keyboard is used to enter a digit into it. To clear the contents of a cell, use the backspace key when it is selected.
It is possible to ‘scribble’ into any cell to make a note of the digits thought to be possibilities. This mode is accessed by selecting a cell using the right mouse button. Then, the numbers on the keyboard toggle each digit on and off.
Every occurrence of a particular digit can be highlighted by double-clicking on any instance of it.
Hints can be requested at any time during a game by pressing the Hint button. In competition mode, each player is restricted to 5 hints.
The current puzzle may be reset by clicking the Reset Grid button. This clears any digits which have been entered since the puzzle began.
A game can be saved by clicking the Save Game button. Any digits which have been entered into the grid are saved with the game so that it can be continued at a later date.