Setting up a skewer: threat (2)
Besides the forcing moves check and capture, a third iteration is threat. With a 'threat' you can think of attacking a piece, a mate threat or threatening to promote. The purpose of the threat is to change something in the position so that a skewer can be performed afterwards. In the examples below, we see an attack on a piece. In Example 2, the attack on a piece is accompanied by a sacrifice.
What do you have to do?
Provide a threat (attack a piece, mate threat or threaten to promote). Subsequently win material with a skewer.