The cells in each row (horizontal) must have all the numbers from 1 to 9, without order. The cells in each column (vertical) must have the numbers 1 to 9, without order. Each domain 3x3, the bold outline, must have the numbers 1 through 9. The game begins with a Sudoku grid, in which a number of cells available for the right numbers. You have to deduce the numbers found in the remaining blanks. The easier the sudoku problem usually starts with many numbers have been filled in, so you will easily find more answers. More and more I find out the number, the more likely you will find the other number.