The board is divided into cells, with mines randomly distributed. To win, you need to open all the cells that don't contain mines. Clicking a cell that doesn't have a mine reveals a number. This number is the amount of neighbouring cells that contain a mine. Using this information, you can determine cells that are safe, and cells that contain mines. Cells suspected of being mines can be marked with a flag using the right mouse button.
To start a new game, you can click on the happy face at the top of the board or use the space bar. The remaining number of mines is displayed in the left corner, and the game timer is displayed in the right corner.
When a number has the correct amount of flags, you can click on the number to open all the cells around it. This is called a chord because in older versions it required pressing two buttons, left + right, at the same time (can be changed in settings). Using chords greatly reduces unnecessary clicks, and is the foundation of efficient gameplay.
No guessing mode (NG)
One of the best ways to learn how to play is to play in no guessing mode. In this mode, a starting position is provided, and you never need to guess to complete the board. If you get stuck, there is a free hint button at the bottom right. Higher difficulty NG boards require the use of more complex logical patterns. Evil difficulty contains at least one advanced situation in every game.
No flags (NF)
NF is a style of playing that does not use flags. A game is won when all non-mine cells are revealed whether the mines are flagged or not. NF players use this to reduce the number of clicks needed to complete a board.
3BV (Bechtel's Board Benchmark Value) is the minimum number of clicks required to complete a board without using flags. 3BV is used to measure the relative difficulty of a board, and the speed you are playing at (often expressed as 3BV/s, or 3BV per second).
To prevent super lucky games, there are 3BV limits for beginner, intermediate and expert. These are 2/30/99 respectively. Games with a 3BV lower than the limits will not be recorded in the time rankings.