First before starting you need to decide what output voltage you want to select, either 120V 1 phase, 240V 1 phase (may be 120/240V output some are wired this way even if the manual calls it 240V only), 120/208V 3 phase or a special 120V only 3 phase mode. If your using it for backup power around the house you most likely want to set it for 120V 1 phase, this is done with a selector knob inside the control panel (open the panel with a flat head screw driver (2 or 3 screws above the gauges) knob is on the right side I think, turn to selected voltage. There is also a voltage selector knob on the front of the panel, it only changes the meter reading, not the output voltage, if your using 120V 1 phase you will want it in V1-0 all other positions should read 0 on the voltage meter above it. Set Current Selector to L1, again this is just for the meter, all other positions will read 0 in 120V mode. To start the engine when your ready use the master selector switch, it is like a car key turn back and hold to pre-heat (only needed when cold), then crank over to start, and release when running, it then should spring back to run. In the run position it draws fuel from the internal tank, if you have an external tank, you can move the selector back one position to run aux fuel, which will automatically refill the onboard tank when the float drops to a certain point. Once running use the knob below the outlet to adjust engine speed, set at 60 hz on the frequency meter, if the frequency meter is broken (common problem), check with a good multi-meter, fine tune the output voltage with the voltage adjust knob. Leave the setting there, and start it next time in this position, the manual says to turn it down and start at the low speed position on start, but this cable assembly is prone to breaking and spare parts are hard to find.
You should be running now, some of these units are wired with the onboard outlets going through the cut off breaker, others are wired direct and the breaker only controls the output lugs. Onboard outlets may be wired as 2 separate 15 amp or a single 15 amp, you will find the manual is not always right on these, note there are mistakes in the output wiring diagram in the manual.
Ike