The Object of the Game
Surprisingly, the object of Minesweeper is not to flag all the mines in the minefield. The object of Minesweeper is to clear every cell in the field that does not contain a mine. Only at that time does the game end.
The distinction made here is important. At the end of the game, Minesweeper will automatically flag any unflagged mines for you. This is an important time saving step when you begin (and you will) to achieve faster times in Expert level.
There will be situations when it will be unnecessary to flag a mine. Some of these situations will be pointed out later. But for now, it is okay to flag all the mines you find. Flagging mines is necessary in most cases to aid in clearing the minefield.
The right mouse button is used to place a flag on top of an uncleared square. Figure 5 shows locations where mines have been found and flagged.
Mines Found and Flagged