What does Judges 4:19 mean?

But Barak pursued the chariots and the army to Harosheth of the Gentiles; and all the army of Sisera fell by the edge of the sword. There was not a man left.

However Sisera fled away on his feet to the tent of Jael the wife of Heber the Kenite; for there was peace between Jabin the king of Hazor and the house of Heber the Kenite.

Jael went out to meet Sisera, and said to him, “Turn in, my lord, turn in to me; don’t be afraid.” He came in to her into the tent, and she covered him with a rug.

He said to her, “Stand in the door of the tent, and if any man comes and inquires of you, and says, ‘Is there any man here?’ you shall say, ‘No.’”

Then Jael Heber’s wife took a tent peg, and took a hammer in her hand, and went softly to him, and struck the pin into his temples, and it pierced through into the ground; for he was in a deep sleep; so he fainted and died.

Behold, as Barak pursued Sisera, Jael came out to meet him, and said to him, “Come, and I will show you the man whom you seek.” He came to her; and behold, Sisera lay dead, and the tent peg was in his temples.