How is a potential difference created between two points? I would like to know how potential difference is created between two points?Is potential difference created by adding more electrons at one side?If that's the case how to add more electrons at one side?
I'm really looking to know what really constitutes potential difference?

 A: In a circuit, an electric field is created. This electric field forces electrons to move. As current must remain constant (since no charge build up is observed), the electric field must be strongest in the materials that are the least conductive (or most resistive). 
As this electric field moves the electrons, they gain kinetic energy. In order to conserve energy, we must therefore say that the potential energy of these electrons has been converted to kinetic energy. Hence, the potential energy of the electron falls. A potential difference in a circuit merely means that work is done on electrons by an electric field as they pass through the circuit and their potential energy changes. Further, we can conclude that since the electric field is strongest in regions with high resistance, the potential difference must be greatest across these regions as well.
This might be a bit confusing since it implies that potential falls in the direction that electrons flow. Since we choose to deal with the flow of conventional current rather than electron flow, potential falls in the opposite direction of current flow.
A: What is potential difference? It's pretty simple, actually.

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*A charge repels other like charges (with same sign). That means, an electron repels other electrons.

*If you at one point have, say, 10 electrons then they will try to move as far away from each other as they can.

*This point with many electrons (that is, this point that electrons are strongly repelled from) is said to have high potential. A point of less repulsion is said to have lower potential.

In this way, electrons will always try to move towards the lower potential. In other words: if there is a potential difference between two points then electrons will try to move because they experience an electric force towards the lower potential.
How can such a potential difference be established? That's also pretty simple, actually.
To create and sustain a potential difference you need something to move charges "the wrong way". That is, towards the point of higher potential. You just need a force larger than the repelling force.

*

*A device that produces such a force is called a voltage source. A battery is a wellknown example. Inside the battery a chemical process creates such a force which pushes the electrons back up to the higher potential point (the negative pole/terminal of the battery). *

*From this point they again want to move back to the lower potential. They do this by running through the circuit ("around" the battery).

*When the electrons reach the lower potential, which is the positive pole/terminal of the battery, they are moved back up again on the higher potential ready to travel once more.


* The exact inner workings of separation and recombination between electrons and ions across the electrolyte within the battery is a topic in itself in the discipline of electrochemistry. But for the electric considerations we can often black box the battery and purely consider its effect without worrying about how it produces that effect. The battery is in this way just a voltage source. 
A: I will try to explain with some examples. There is never a potential difference when there is equilibrium.
You can think of it as a height difference. Think of positive potential as a high point and the negative one as a low point or ground. So there is a height difference. A thing at the high point is bound to come down.
Similarly, whenever there is charge imbalance, a potential difference is created. I tried to explain as well as I could but the question of exactly how it is created is kind of an abstract thing. It's like asking how the height difference is created between the two points.
Hope it helps.
