generators
hi there parsec, here a very simply explanation with going into details:
Function generator - used to put out sine waves, square waves, saw tooth waves
Signal generator (wide band) - used to inject signal in various stages of amplification. signal frequency depends on the RC network.
Audio generator - as what it implies.
other guys could probably give you details.
you ask how could you use the signal generator, well all you to do is inject the signal to the base of the transistor of a certain stage which you suspect to be defective and listen to the tone signal. if you dont hear anything then check that transistor for proper voltages and all component attached to that device.