Simply fill out the squares so that every row, every column and every 3*3 grid contains all of the digits 1 to 9.
Using Wolf Sudoku
Follow the links in the menu ("Easy", "Medium", "Hard" or "Absurd) to select a puzzle of the desired difficulty level. Although they aren't clearly visible, the empty squares with the blue background contain two entry fields. The lower one is where you type in the value you believe belongs in that square. The upper one is simply a scratch-pad where you can keep track of the possible values. The scratch-pad area has enough space to enter 6 possibilities. This is normally plenty, but in some cases you might find it easier to use a notation to indicate which numbers can't go in a particular square. We suggest using "!" as an indication of "not", i.e. "123589" indicates these values may be used but, "!4!6!7" indicates the same thing in reverse! It's up to you, the scratch-pad is a free text area for your own help in solving the puzzle.
At any stage as you fill out numbers you can click on the "check" button and it will indicate any incorrect squares by a red background and set any correct ones to yellow background.
The "help" button automatically fills out the next square that WolfSudoku finds following it's programmed strategy for solving. WolfSudoku has many of the well known strategies programmed and they are processed in order of simplest first. The strategies programmed are good enough to solve all of the problems up to the "hard" level. In the "Absurd" class of puzzle, the program switches to a recursive method of simply trying every possibility (optimized by still applying the known strategies first).
The "solve" button simply completes the entire puzzle.
From the main screen, there is an "Empty Field" link, which allows you to enter your own puzzle.
The menu point "Large" or "Small" simply lets you switch between
a larger format or smaller format of the puzzle. Small is optimized
for resolutions of 1024*768.