Answer:
Step-by-step explanation:
If generator really means alternator as used in cars, the following can be said:
The rotor is fed with a variable voltage ranging from 0 volt to 12 volts. The 2 brushes (fixed, not rotating, like the stator) make contact with two rings that are rotating with the rotor. The rotor acts like a fixed magnet, but the magnetic field strength is constantly updated to provide a constant output voltage, even if the load current change or the motor speed change.
The stator is basically 3 coils and 6 diodes that convert the 3 phases of AC output to an almost ripple-free DC.
Note that as more energy is extracted from the alternator (for example, adding 10 amps by turning on the headlights) the shaft resists more rotation. This can be easily tested by holding an alternator in your hand, and trying to rotate the shaft by hand with no load (rotate easily, keep rotating for a few seconds), then short-circuiting the output (much harder to rotate, stop rotating immediately). The quest for magical perpetual energy where a motor is powered by an alternator is a child's dream.