Take the defender
In previous lessons, all defenders were defending pieces. Sometimes a defender guards a mating square. If you manage to capture that defender, the end of the game is near.
You see that in example 1.
Example 2 uses a sacrifice. By giving away points, White wins a lot in the next move: he can checkmate his opponent and win the game!
What do you have to do?
Take the defender of a mating square.