The image below shows a Sudoku Grid. There are 81 small squares arranged in a 9x9 grid. That makes 9 rows and 9 columns. The grid is also divided into 9 3x3 minisquares.
To solve the puzzle, fill the grid with the numbers 1-9 using each number only once in each column, row and minisquare.
You don't use arithmetic to solve Sudoku, just logic. As long as the puzzle has been designed properly, there will be only one solution and logic alone will let you know which numbers to put where.