The Two Basic Sudoku Techniques: Singles (One Number per Cell, One Cell per Number)
Easy to Medium puzzles can be solved with just these two ways of spotting a move.
A cell with only one possible number (naked single)
For a given cell, rule out the numbers already in the same row, column and box. Sometimes only one number is left. That cell must be that number.
A number with only one possible cell (hidden single)
When there is only one cell left in a row (or column, or box) where a number N can go, that cell must be N. This works because N already sits in other rows and columns, which rules out the other cells in that row.
How to proceed
Go box by box. Take each number not yet placed and ask, "Where can this number go?" When you narrow it down to one cell, fill it in, then move on to another number or another box.
Levels where these two are enough
On this site, Kids, Easy and Medium are built so that these two techniques alone can solve them.
More articles: Sudoku Rules and How to Get Started / How to Use Notes (Candidates) in Sudoku / Sudoku Techniques: Pairs (Naked Pair and Hidden Pair) / Sudoku Techniques: Boxes and Lines (Pointing Pairs) / Sudoku Techniques: X-Wing / Sudoku Techniques: Trial and Error (for Demon, Hell and Abyss) / How Kids Can Play Sudoku (6×6)
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