A normal game starts with you selecting the number of squares you want to get displayed at the start. Then you hit the 'Start Game' button. The game will then create a puzzle for you and randomly display that many squares.
A custom game starts with you selecting the squares that you would like to be filled in. After you have selected the squares you can hit the 'Start Game' button to play Sudoku.
A Sudoku Solver game starts with you dropping the values (1-9) on the squares that you would like to have filled out. When you have completed all of the squares you want you can hit 'Start Game' to play Sudoku. The purpose of this game is to allow you to take a Sudoku puzzle you have found else where and solve it.
Buttons
Help: Will solve a single square in the puzzle
Undo: Will undo the last square you solved
Done: Will reset your game and take you back to the start screen
Validate: Will check to see if the puzzle you are working on is completed
Solve Puzzle: Will solve the puzzle when you get stuck
CLR: Will clear any square that you drop it on