In an electrical power supply, such as a battery, an electro motive force increases the electrical potential (E) of electrons, as they are transferred from the positive terminal of the battery, to the negative terminal. The increase in electrical potential, is a measure of the energy supplied per Coulomb, as the electrons are transferred between the battery terminals.
As the electrons travel through the resistor, their electrical potential drops, as resistance converts their electrical potential energy to heat.
Electrical potential is similar to gravitational potential. Gravitational potential is a measure of the energy per kilogram supplied to an object, when it is raised above the Earth's surface. Electrical potential is a measure of the energy supplied per Coulomb, as charge is transferred between the terminals of a power supply.
Note, in the example above, we are ignoring the resistance in the conductors. So the animation shows all of the potential energy of the electrons being converted into heat, as they pass through the resistor. In reality, the conducting wires do have a small amount of resistance and so the electrical potential of the electrons, does drop by a small amount, as they move along the wires.
Also note, that the above description uses true electron flow. If we were to describe the process in terms of conventional current flow, we would consider the potential of positively charged particles being increased, as they are transferred inside the battery, from the negative terminal to the positive terminal and then decreasing as they move through the resistor. This is illustrated in the diagram below.