How to Play Sudoku. A Beginner's Guide
Sudoku, step by step. By the end of this page you'll be ready to start an easy puzzle without anxiety.
1. Understand the grid
Nine rows, nine columns, and nine 3×3 boxes. Each "group". row, column, or box. must contain digits 1 through 9 exactly once.
2. Scan one digit at a time
Pick a digit. say 5. and check each row, column, and box. Find spots where 5 can only go in one cell. Place it there. Move to the next digit. This is by far the most efficient early-game tactic.
3. Look for naked singles
A cell with eight of the nine digits already in its row, column, or box has only one possible value. These are called naked singles. After every placement, re-scan the cell's row, column, and box for new naked singles.
4. When to start using pencil marks
When scanning stops finding moves, write small candidate digits in each empty cell. This is slow at first but unlocks every advanced technique. See pencil marks.
5. Never guess
Every Sudokly puzzle has exactly one solution reachable with logic. If you're tempted to guess, you've missed something. Back up, scan again, and trust the puzzle.