How to play Sudoku
Nine digits, three simple constraints, and a place to begin.
One grid. Three simple rules.
Fill the 9 × 9 grid using the numbers 1 through 9. Each row, each column, and each of the nine 3 × 3 boxes must contain every digit exactly once. The numbers already printed on the board are fixed clues. You cannot change them.
Start where the clues are.
Choose a row, column, or box with many numbers already filled in. List what is missing, then test each empty cell against its other two units. If all but one number are ruled out, you have found a naked single.
Try one move.
In the example below, the highlighted cell is in row 5, column 5. Its row is missing 2, 5, 6, 7, and 9. Its column rules out 2, 6, 7, and 9, leaving 5. You can place 5 without guessing.
Let the next move follow.
After placing a number, check the row, column, and box it touches. One new digit often makes another placement possible. You do not need arithmetic, speed, or a perfect memory. When the answer is not clear, add candidate notes and move to another part of the board.
Use the controls at your pace.
Select a cell, then choose a number on the pad or your keyboard. Notes toggles small candidate numbers. Undo reverses your last edit, including any notes it removed. A hint explains the next logical step before you decide whether to apply it.