Electricity is based on the flow of electrons from one point to another in a conductive material. This flow of electrons is called current. As with most thing in nature this flow occurs from an area of high population to an area low population. In this case from a high source of electrons to a low source of electrons usually ground.
The difference between these two points is called the potential difference or the voltage, it is a measure of the potential for electrons to flow from one area to another.
The flow of electrons can be impeded by the resistivity of the conductive material through which the electrons are flowing, a resistor is a device which restricts the flow of electrons. The relationship between Voltage, Current and Resistance is governed by Ohm's Law.