The buttons

-/+
These buttons change the size of the sudoku.

Print
Prints the sudoku according to your print settings.

Check
This checks the numbers you've entered so far. Numbers shown in green are correct and numbers shown in red are wrong. If a number is shown in yellow this means that the number may or may not be correct, the sudoku solver doesn't think it's possible to solve this square with the current visible information.

Hint
Gives you an extra clue. The number you receive is always such that you could find it with simple logic - because of this, hints may not always be available.

New
Starts a new sudoku from the same level.

Restart
Restarts the current sudoku.

Play with high score
Starts a high score game. In high score games you are not allowed to see which sudoku you are currently solving. For obvious reasons solutions and hints are not available in high score mode.

Show solution
Opens the solution for the sudoku id in the textbox. The solution is opened in a new window where you can print it.