As a charge moves round a circuit from the positive to the negative it loses energy. There is a problem here. As you know an electric current is a flow of negatively charged electrons and these flow away from the negative terminal of a supply, round the circuit and back to the positive terminal. However the 'traditional' view of current flow is from positive to negative and we will take that view when looking at the energy of electrical charge.
The electrical potential energy of a unit charge at a point in a circuit is called the potential at that point
Potential difference between two points in a circuit is the work done in moving unit charge (i.e. one coulomb) from one point to the other.