Generators contain permanent magnets whereas alternators require some amount of current to create electromagnets. You can get power by running straight from the generator/alternator; however the output voltage is dependent on it's speed of revolution. One thing that may be able to be salvaged from disabled/abandoned autos is their voltage regulators. They work in conjunction with the alternator to produce a constant output voltage that doesn't change as the engine speed changes.
Offered by Ron.
The alternator is what converts the mechanical power to electricity. The alternator generates AC current. If you want to run an application directly from the generator instead of from the battery the output of the alternator needs to be rectified and filtered with diodes and capacitors (but this may be part of the battery charging circuit already) to produce DC.
Offered by Michael S.
A common mistake that many make is to think that generators or alternators create electrons. This is not the case. Generators or alternators are like a water pump. You turn the shaft and the electrons present in the conductors are pumped along as these conductors are forced to cut across a magnetic field. The electro-magnetic pulse moves a magnetic field that causes electron flow. With a generator or alternator the conductor moves and the field is stationary or vice versa using the same principal as above.
Offered by Mike.