Think of it in terms of water flowing in a garden hose. You turn the water on and it flows out the end of the hose. On the electricity side you would have electrons flowing, you have conductivity. If your hose has a leak, water flows out. Water and electricity always take the easy way out. In this case on the electricity side you have a leak also. The electrons are flowing out the hole and you have less at the end. It could be some one stepping on the hose too and that would be a short. In either case you have less flowing and a resistance to flow. You have more resistance, or less conductitivy. If the hose is cut you have no water, you have an open. That's alot to think about, maybe Mike could explain it more rednecky.