A sacrifice in chess is when you momentarily give up a piece in exchange of a future outcome, probably taking another piece, gaining a better position, or start cooking a checkmate. Sometimes you know what you are getting, sometimes you don't.
Don't be afraid to give up your pieces if it ultimately leads to winning the game. Pay particular attention to checks, captures and threats that sacrifice something for checkmate, future material gains or a strong attack.
Look at the queens clashing! Can you find a sacrifice for White that will win this queen battle?
White sacrifices the bishop to force Black's king away from the queen's protection. Let's capture Black's queen!
White wins a queen for the sacrificed bishop.