Answer:
The difference in electrical potential is the difference of electrons from one site with respect to another, when this occurs those of the site where there is more they move to the site where there is less. This is what is known as electric current. The difference of electrons from one site to another is measured in Volts, the more volts the more difference there is in the amount of electrons from one site to the other and therefore more electrons will run to there as soon as they can.
The upper vessel has a potential (in this case gravitational) and the one below another. If the two are joined with a pipe, a stream of water starts from one to another container. This happens, for example, with any electric (electric-generated) battery, by joining the two (+) and (-) poles as they are at different electric potential an electric current (of electrons) starts between them.
An electric generator maintains a difference in electrical charges between two points, called poles, terminals or terminals, so this electrical energy can be converted into other forms of energy.