The brief instructions on this page allow you to dive right in to solving built-in puzzles. There are many more useful features you will want to know about. Be sure to check them out when you are ready.
Zudoku starts up with a new puzzle ready to solve as shown here. The large black numbers are the starting numbers. The small numbers 1 through 9 in empty cells are for selecting a solution number with the mouse or for your "notes".
The green dots turn to red if there is an error in the corresponding row, column, or box. In addition, cells with conflicts will have a red outline.
Left-double-click on the small number in the cell you want to solve. The cell will have a large gray solved number.
Left-click anywhere in the cell. The cell will return to its previous status.
Right-click on the small number. The small number will turn red. Right-click again to return it to "unknown" (gray).
Left-click on the small number. The small number will turn green. Left-click again to return it to "unknown" (gray).
On the menu: click Puzzles then Next Puzzle.