Think of a water tower. The water in the tower, combined with its height, is voltage. This flows down through a pipe with a valve that restricts its boundless flow out of the tower, if the bottom fell out. Consider the valve as resistance. The more you open the valve, the less resistance to the water flowing through the pipe. The actual flow of water through the pipe is current. And you can relate that to the current of water flowing in a river. So, all of this upholds the concept of Ohms law. The voltage, divided by the resistance, equals the current flow. Again, reduce the resistance, the more current flows. And, like a battery, as the water level decreases in the water tower, the less push it has to push the water out of the pipe, and the voltage decreases.
It's all physics and there are many other corollaries. This one has been used for years to teach students. The ones provided by others regarding voltage step-up and step-down are reasonable.
JByers - 40 years in Electronics Engineering.