Learn / Sudoku
How to start a Sudoku puzzle
Scan for nearly complete rows, columns, or boxes. List the missing digits and check their crossing units. Work on the area with the fewest candidates, then scan again after each placement. Avoid guessing early: a single correct placement often unlocks several others. The worked example below shows a placement you can prove.
A checked example
Row 1, column 7 takes 3. Every other digit is already excluded by its row, column, or box.