It comes from a negative charged plate and a positive charged plate being immersed in a electrolyte solution, this could be an acid such as the sulfuric acid of your car battery, or a base such as in alkalyine battery. When connected to a load, a flow of electricity moves from the battery to the load.
Electric potential difference is the difference in the electric potential (V) between the final and the initial location (terminals of the battery) when work is done (the battery powers some device) upon a charge to change its potential energy. A battery converts potential energy (stored energy) into electrical energy.
When a circuit is generated when the battery is connected to a load, it causes current to flow, such that there is an electrical differential between the negative and positive terminals of the battery. Voltage can be viewed as electrical pressure, analagous to water pressure, while current can be viewed as analagous to the flow of water through a pipe (the flow of electricity (electrons) through a circuit- which is current)