Rolling resistance is composed of all the components on the coach that have to rotate in relationship with the ground. If you look at your tires, they have a flat spot where they contact the ground. There is a bulge at the bottom of the tire where it is distorted by the contact with the ground. As that tire rotates, that bulge moves as the tire sidewalls are flexed causing the tire to warm up. Again, that heat is the manifestation of the losses caused by rolling.
Potential energy is what moves a weight from one height to another.
Just walk up a flight of stair to experience expending potential energy. The more weight, the more energy it takes. If you climb over a mountain pass, you have invested a tremendous amount of energy simply moving your vehicle up the hill. In an ideal world, that energy is recoverable, because you can coast down the other side, but in reality, you end up wasting that energy by either using the engine or the brakes to slow you down. When traveling in hilly country your mileage will be significant and negatively affected.