Learn Sudoku

First the methods (how to search and how to take notes), then the techniques, from the simplest to the hardest.

Methods

1. Basics and vocabulary — The rule of the game and the words the other articles use.
2. Scanning — How to find numbers just by looking at the grid.
3. Pencil marks — What to do when scanning stops finding numbers.
4. Where to start — The order to search in, and what to do when you get stuck.

Techniques

1. Hidden Single — When there is only one cell in the row, column or box where a number can go.
2. Naked Single — When a cell has only one possible number.
3. Pointing — When, in a box, a number only fits in one row or one column.
4. Claiming — When, in a row or column, a number only fits inside one box.
5. Naked Pair — When two cells of a unit have only the same two candidates.
6. Hidden Pair — When two numbers only fit in the same two cells of a unit.
7. Naked Triples and Quads — When three or four cells of a unit have, between them, only three or four candidates.
8. Hidden Triples and Quads — When three or four numbers only fit in the same three or four cells of a unit.
9. X-Wing — When a number, in two rows, only fits in the same two columns.
10. Y-Wing — Three cells with two candidates that, together, remove a number.