What is AC electricity:
The easiest explanation of electricity is a water dam. Picture a dam with a pipe at the bottom letting water out. The higher the dam the more pressure there is at the bottom of the dam the water comes out faster because it is under more pressure. So, pressure is Voltage they are one in the same.
Increase the size of the pipe at the bottom of the dam and you increase the amount of water coming out or current flow. Current flow is Amperage.
Together you arrive at gallons an hour or Watts. Reduce the height of the dam and you reduce the pressure or voltage, and you reduce the current flow. Make the size of the pipe bigger you can adjust for the drop in dam height and increase the current flow. These two factors equate to gallons per hour VOLTS X AMPS = WATTS.
To explain how AC electricity is made we need to go back to our dam. The generators run at a fixed RPM making alternating current at 60 cycles a second or 60 hertz. Power is created when two magnetic fields pass through one another or cutting lines of flux. The one fixed is called the stator and the one rotating is the rotor. Every time the south pole magnet passes by the other north pole magnet it makes a spike of electricity. When the north pole goes by it makes a spike of electricity in the opposite direction creating alternating current. The rotor has an electromagnetic field commonly called the exciter. By adjusting the power to the exter field you can adjust the amount of power coming out of the stator windings. It is how all generators work. the alternator on your engine is not too much different with the exception of a series of diodes that only allow the current to pass in one direction making DC current.