Let a charge q be placed at a point O. A and B are two points in the electric field. When a unit positive charge is moved from A to B against the electric force, work is done. This work is the potential difference between these two points.
The potential difference between two points in an electric field is defined as the amount of work done in moving a unit positive charge from one point to the other against the electric force.
The unit potential difference is volt. The potential difference between two points is 1 volt if 1 joule of work is done in moving 1 coulomb of charge from one point to another against the electric force.
The electric potential in an electric field at a point is defined as the amount of work done in moving unit positive charge from infinity to that point against the electric forces.