Converters ---convert shore power(when you have electicity)from110volt to 12volt.I am not good at explaining things.When you are plugged in all your lites run on 12volts in most cases also your furnace
and some roof fans,so the power is changed for this purpose.Your wall out lets stay at 110 volts . If you have a battery
charger the power not being used will go to charge batteries,if you are using lots of power then your batteries will kick in to help with the power demands.
We have on this forum some people who are really good at explaining things and they will chime in with there knowledge.