It will make the car easier to start and get better gas mileage.
You simply plug it into the harness then connect it to the unported (vac all the time) port on your carb with a short piece of vac hose. Some guys drill a hole in the mainfold for a slightly cleaner look.
For a map sensor just pull one off pretty much any GM car in the wrecking yard. I got one off a 3.8L V6 Pontiac. Just make sure the plug matches the connector on the MSD harness. Take a picture with you. If you don't want to get one from the wrecking yard you can buy them new for $50-$60.