Basic patterns
The 1-1 and 1-2 patterns along a wall.
When a number touches exactly as many hidden squares as its value, all of them are mines.
When a number’s mines are all flagged, every other hidden square around it is safe.
Compare two neighboring numbers: if one’s hidden squares are a subset of the other’s, the difference tells you about the extra squares. This is how the 1-2 pattern works.
Practise it
The Hint button on every puzzle explains the next step in the same plain language, so you can learn as you play. Play a Minesweeper puzzle.