When Eileen Leahy noticed Sam Winchester chasing her, she used the spell to trap him, mistaking him for the Banshee she was hunting. Once Sam proved that he was human and a hunter instead of a Banshee, Eileen broke the spell and freed him.
In order to kill the Banshee, the Winchesters and Eileen set up the spell in Mildred Baker's room, thinking Mildred was the next target. As the Banshee attacked Dean Winchester, Mildred activated the spell on Eileen's orders, trapping the Banshee. Eileen then killed it with a gold knife.
Two sigils must be painted on opposite ends on the room. The target must be drawn between the sigils and one then activated by slapping a bloody palm in the middle of one of the sigils. The target is then pulled up against the second sigil where it is immobilized and powerless. The spell can be broken by breaking a line on the trapping sigil.