Electrostatic potential , at any point, in an electric field is defined as the amount of work done in moving a unit postive charge between infinity and that point, without any acceleration, against the electric force.
Every point around a source charge(q') is characterized with electric potential, which is given by;
V (r) = (1/ 4Πεo )q'/r
If instead of bringing a unit positive , we bring a charge 'q' from infinity to that point, work done W in doing so is given by,
W = q x V(r) = (1/ 4Πεo )qq'/r
This work done is termed as 'electrostatic potential energy' of the charge q in the field of charge q'.
We can also say that the electric potential, at any point, in an electric field is the potential energy of a unit positive charge placed at that point.
We hope this clarifies your doubt.