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Terminology

Electric Potential - Magnitude of difference between positive and negative charges in a circuit. Basically, like the difference between a high pressure and low pressure area of water. Since the water in the high pressure area will want to move to the area of low pressure, the water will flow. A very positive charge will try to move towards a negative charge if the electric potential is high (though the actual flow of electrons is in the other direction).
Symbol: (V)
Units: Volts (V)

Current - Amount of electricity that flows through a certain point. Like the numbers of gallons of water that flow past a point in the water wheel scenario.
Symbol: (I)
Units: Amperes (A)

Power - The rate at which electrical energy is transferred. It is like the amount of wheat that can be ground each second in a water wheel.
Symbol: (P)
Units: Watts (W)

Resistance - Measures how the device or material reduces the electric current flow through it. Think of resistors as the different diameters of the pipes in a water wheel system - larger pipes allow more water to flow while smaller pipes provide more resistance to the flow of water; without the proper diameter of pipes, too much water would flow, and the wheel could break. If too much current flows through a circuit due to a lack of resistance, components could overheat or even explode.
Symbol: (R)
Units: Ohms (Ω)

There are two important formulas used in electrical engineering and physics. One, called the Power Law, is P = I * V. Power is equal to the current times voltage. The other is Ohm's Law, V = I * R. Electric potential is equal to current times resistance. Since both formulas use similar variables, they can be modified to get desired results.

For example, if an engineer knows the power and the current of a circuit and is trying to find its resistance, the P = I * V formula can be changed to P = I * (I * R), or P = I^2 * R, which can be rearranged to be R = P/(I^2).

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