Potential difference is the energy transferred per unit charge that passes between two points. A cell or battery transfers chemical energy to the charge. A component, such as a lamp, transfers electrical energy from the charge to other stores.
Charge is measured in coulombs, C, and energy in joules, J. One volt is one joule per coulomb. So if the potential difference across a component is 1 V, each coulomb of charge that passes through it transfers 1 J of energy.
A 6 V battery gives 6 J to every coulomb of charge that passes through it. A 12 V supply gives 12 J to each coulomb. The higher the potential difference, the more energy is transferred for each coulomb.