To begin, let's look at the basics. If I have an object with a positive charge (call it P) and an object with a negative charge (call it N), they will attract each other, and if you have two P's or two N's, they'll repel each other. The energy that goes into their motion comes from the forces between them. With a P and an N, it's like there's an imaginary spring between them that's stretched beyond its natural length, and it wants to pull them together. With two P's or two N's, you can imagine the spring is compressed a lot, and pushes the objects away.
Scientists call this electrical potential energy, because it's the energy that charged objects have based on their positions relative to one another, just like gravitational potential energy is the energy that things with mass have based on their positions relative to one another. In other words, charged objects create a "potential field" in which other charges have electric potential energy, in the same way that the Earth produces a gravitational potential field and things in the field have gravitational potential energy. The value of the potential field at a certain point is the amount of energy a charge has divided by the amount of charge it is (e.g. a 2 Coulomb charge with 100 J of potential energy is in a 50 V potential field). We say that electric potential is "electric potential energy per unit charge."
We say that there is an area of high potential when there are lots of positive charges around, and we say that there is an area of low potential when there are lots of negative charges around. From this definition, it's clear to see something with positive charge will want to go from high potentials to low potentials, and something with negative charge will want to go from low potentials to high potentials.
Hope that answers your question,
(published on 03/21/11)