Electrical charges come in two forms that we have designated as being positive + and negative-. The opposite type charges attract and the same type of charges repel. This fact makes it possible to exploit these little guys and make them do work for us! By separating unlike charges we make electrical pressure since the like charges now want to get as far away from each other while being attracted to the opposite type. We need to do work to separate these charges and we get work back as they move back towards electrical equilibrium, i.e., the same number of + and - charges.
Voltage can be considered to be an electrical pressure that moves electrical charges.
Current is a measurement of how many charges are flowing due to the voltage pressure.
Resistance will inhibit the current flow.
If you think of a flowing water analogy, Voltage is the height of the water, Current is how much of the water flows by in a given time, and Resistance is the paddle wheel you put in the water that inhibits the flow, but that makes it possible to get work out of the flowing current.
The power delivered is equal to the pressure applied and the amount of current flowing.
V=IR: The voltage is equal to the current (I) times the resistance (R). Notice this relates to the discussion above. The higher the voltage, the greater the current, and solving for I. This is known as Ohm's Law
I=V/R : we see the relation that the higher the resistance, the lower the current..
The Power delivered is given by P=IV or P=I2R. This is known as Watt's Law.
That is the fundamentals. The rest is just explaining how the pressure can be made and the applications...