How does a battery creates voltage or potential difference?

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)