Cells can be empty, contain a number, a mine, or a question mark.
That number represents the amount of mines adjacent to the cell
(including diagonals).
Left-click/tap a cell to reveal it.
Right-click/long-tap a cell to place a flag. Right-clicking again will
remove the flag and add a question mark, and a final right-click will
remove the question mark.
Chording: Left-click on a revealed number when you've
placed flags equal to that number around it to automatically reveal
all remaining adjacent cells. This speeds up gameplay but will
detonate mines if you've misplaced a flag! Note: Chording is disabled
if any adjacent cell has a question mark.
Once all non-mine cells are revealed, the game is over.