1 move checkmates with few pieces
When you checkmate your opponent you win the game (1-0). Checkmate occurs when your opponent's king is under attack (check) and has no way of getting out of danger. The three ways of getting out of danger when your or your opponent's king is in check are by capturing the piece putting the king in check, moving the king to a safe square, or putting a piece between the king and the piece attacking it.
Here are three examples of checkmate.