I urge you to buy a multimeter (a $10 one is good enough) and find someone to teach you how to use it. For starters, you pretty well need to measure the voltage on the batteries while not charging, charging from engine, charging from AC power to the converter in order to know all these components are working.
When you get a chance play around with the system, switching off the inverter, to learn which outlets, lights and appliances are powered from the inverter. Also by AC from shore power. The remainder must be DC - labels for them should be made beside the fuses so it won't be confusing next time.
You cannot be shocked by touching 12 volts DC with your fingers. If you spit on two fingers and touch the battery terminals you will prove that to yourself.
Don't ask your teacher about measuring current (amps) until next year - beginners often burn out the current ranges on the meter so best not to use them yet.