Mostly they "invert" or "convert" 12V DC power to 110-120V AC or vice versa to run your electric "stuff".
Depending on what type of power your appliance needs, and which source you want to use,
you might be able to just plug it in and away you go, or you might need an extra piece of equipment.
My van has 2 types of electric power source outlets. Some look like cigarette lighter sockets, and I also
have a couple that look like regular household wall outlets.
My cig-lighter type outlets are located up front at the dashboard, and in the rear entertainment
cabinet near the bed.
The ones up front run off the vehicle 12VDC battery (the one that starts your engine) and can
run things that need 12VDC power. I sometimes use them with a 12VDC to 110VAC mini-inverter to
recharge stuff while we're driving. Low draw only. Like camera batteries or cell phone charging.
I never use the vehicle battery outlets to charge stuff when the engine isn't running. That way
I don't discharge the vehicle battery too much that I can't get the van started.
A dead vehicle battery is mostly a bad thing.
The rear ones in the e-unit draw from the house or coach batteries. The coach batteries are separated
from the vehicle battery by a battery separator or isolator, so that you can discharge them without
draining your vehicle battery. I enable them via a "battery enable" switch at my monitor panel.
They can run things which require 12VDC power. For example,
I have a small dirt sucker vacuum cleaner that uses 12VDC power and has a cigarette lighter style plug,
so I can plug it into one of the e-unit cigarette lighter outlets, enable the coach batteries, and use it
to clean up little spills and messes.
I also use 2 slightly larger draw 12VDC to 110VAC mini-inverters to run my laptop and LCD TV. I have a 100W
and a 150W mini-inverter for these 2 uses. Since most of my electric "stuff" uses well below 50W
of power each, the 2 mini-inverters are more than enough to handle their draw.
You can plug the mini-inverters into a cigarette lighter type plug, and then plug (into them) a 110VAC type
2 or 3 pronged plug from the appliance. Very useful, for me, at least. They get the most use in my van.
They can be purchased at Canadian Tire, or Best Buy, or Radio Shack, or most major electronics stores.
Some folks on here have either bought vans with much larger inverters already installed or added them
later to run larger draw items like their Microwave ovens or electric heaters, etc..
The coach batteries will (slowly, we hope) drain with use, and can be recharged at least 3 different ways,
but that's another topic. 4 ways, if you add a solar charging system. Again, another topic.
The ones that look like house outlets, are 110-120V AC output when the van is plugged into
shore power at a campground, or with an adapter into my house's outside 110V outlet (using
the big black cable with the funny plug), or when I'm running my 2800W Onan on board generator.
The shore current 110VAC just passes through the inverter in the van and comes out at the van outlets,
or, the generator power is inverted/converted to 110VAC and comes out at the van outlets as 110VAC.
Anything with a 2 or 3 pronged plug which uses 110VAC power can run when plugged into them.
I'm going to start making coffee with a drip maker that uses 900W so I'll be running my
generator for 10 minutes while the coffee maker is plugged in to one of the house outlets. Also,
my microwave is plugged into a house type outlet, and I'd have to be on shore power, or running my
generator to make popcorn in it. It draws more watts than the mini-inverters can provide.
Also, my A/C unit needs shore power or the generator running to work properly because of it's
larger current draw.
So, does that make any sense at all?
I'm not an expert, but that's my view of the world as it relates to class B vans.
If it doesn't rain tomorrow, I'll try to add a couple of pics of my usual setup.
Oh, the coach batteries can be charged by the engine/alternator combo when the engine is running,
by plugging the van into shore power with the "battery enable" switch enabled, or
by running the generator for a period of time. In a 2002 Roadtrek, anyway.
You can move slightly farther "off the grid" by adding a solar battery charge system, but you'll
have to ask VernM or markopolo for more info about that.