The objective of sudoku is to populate all the cells in the board with the numbers 1-9, obeying these rules:
  1. Each row can only contain each of 1-9 once.
  2. Each column can only contain each of 1-9 once.
  3. Each 3 by 3 grid, as demarcated on the board, can only contain each of 1-9 once.
That's it, and it can be very very difficult.  

You will notice that every game starts with some cells filled in.  Those are the givens.  Each board can only have 1 solution.

  • You can navigate around the board with the keyboard arrows.  
  • The 1-9 numbers enter values in a cell.  0 clears the cell.
  • You can enter more than one value to take notes.  If you are on a cell and think "2, 3, or 8 can be in this cell", just hit those numbers.  Hitting a number again removes it from the notes.  0 clears.
  • With the mouse, clicking a cell bring up the input pane.  To close the pane just click another cell, or click the "x" icon.  The empty square icon clears the cell.  The numbers work the same as the keyboard numbers.
  • You can generate sudokus of varying difficulty from the "Generate New" submenu.
  • The “Show Hints” options shows you all the possibilites for every cell on the board that is not given or filled in.  Its like taking notes, except the program is taking notes for you for every cell, and it doesn’t make mistakes. When showing hints, just click the hint you want to select.
  • ‘Verify Solution’ is only available after you fill in all the cells.  The clock stops and you can see if your solution is correct.  If not, the errors are highlighted.
  • ‘Show Errors’ highlights mistakes in red.
  • You can get a hint with the “Uncover One” option, and you can give up with the “Uncover Board” option.