Potential energy can be defined as the capacity for doing work which arises from position or configuration.In the electrical case, a charge will exert a force on any other charge and potential energy arises from any collection of charges.
Where is this potential energy stored and how?
That actually gets a bit tricky at the advanced level, but at the basic level, you should find somewhere in your textbook the equation $U = \int d^3x \left(\frac{1}{2} |\vec{E}|^2 \right)$ (maybe with a different constant up front, depending on what system of units the book is using). So at any point in space, the electric field $\vec{E}(\vec{x})$ at that point "stores" an amount of potential energy $\frac{1}{2} |\vec{E}|^2$.
