You are correct with the terminology... "shore power" is plugged in. There are a few of those terms you'll catch on to as you keep reading here.
And yes, if everything is working properly, the house batteries should be charging when connected to shore power. Does that rig have a panel readout somewhere that shows you the current battery level?
If you found your RV's interior breakers (they all have them in different locations) and nothing seems to be tripped, finding/testing your converter and the house batteries are the next step. The converter is what changes power from 110v AC incoming (from the plug) to 12v DC (to the battery or batteries) and charges them. That charge allows the 12v items throughout the RV to keep running, as Wally indicated.
In most Class A's including your 1990's Bounder, the house battery (or batteries) are almost certainly in a "basement" storage compartment that is accessible from the outside. They should be deep cycle 12v batteries (often sold for golf carts, marine usage, etc.) and can be removed and tested for free at almost any auto parts store. You can also check the yourself in a simple way if you have a multimeter (small handheld device to check electrical connections)... a good/charged 12v battery usually measures around upper 12's to 13 volts.
The converter could be located in a variety of locations too... under an entry step, behind a cabinet panel somewhere, perhaps near that fuse block you located... although not likely above the door.
It looks like a metal box, wires attached, and will have a small fan that kicks on when it's working. If you can find the converter and learn its make/model, we can help test and troubleshoot that device also. Camping World is fine, but many maintenance items can be bought just about anywhere (Walmart, auto parts stores, etc.) or ordered online (Amazon and the like) for much lower prices than any RV-specific place.
You might want to start reading some
articles in our forum library, to familiarize yourself with RV systems in general. Feel free to keep browsing the general discussion areas, jump into any ongoing conversation, or post new questions of your own as well!