You cut a little piece of pivot cup off of your big strand, put it on the sharp part of the hangar, or even inside of the smallest hole on the baseplate(thats what Blackriver-Trucks do) and then if you're doing the pivot cup on the sharp part, you'd want to push up to your body until the pivot cup is on tight, if you're doing the pivot cup inside the baseplate, you'd want to push the pivot cup in the baseplate until it is in there enough where you can put the hangar on, and you still want it to be flush with the trucks.
What does it do? well it helps for better turning system!