When you press the 'Check Moves' button, any squares in the Main Puzzle Board that have been filled out will be checked against the solution. If any numbers are wrong, then you will be asked if you want to see which squares are incorrect. Answer yes, and the squares will be marked in red. Squares that have been marked as Possibilities for numbers are not checked.
Hopelessly stuck? If you press the 'Show Solution' button, all the squares will be filled in with the correct numbers. The game doesn't have to be over, though. If you press the button again, then the solution is hidden and the numbers revert back to what they where previously, so you can continue.
Clears the board and takes you back to the start.
Automatically remove Possibilities
If this is ticked, then when you enter a number as 'solid' (not a possibility) then that number will be removed from the possibilities of the same row, column and 3x3 square.
Allow incorrect Moves
If this is not ticked, then when you enter a number that is not correct, it will flash and immediately be removed.