I've felt overwhelmed many times during my conversion. I think many of us have. Sometimes the best thing to do is step away for a day or two and let all you've taken in settle.
It's helpful when you start a thread to provide as much clarity and detail in what your issue is and what you're seeking.
If I interpret your post correctly, you are asking for information on how to install shore power and 12v power initially, and then solar afterwards. Is that correct?
You apparently also have a unit, yet we need to know details about the unit. Is it an inverter, a charger or a combination inverter/charger. What are the ratings.
If it's an inverter, it will be the number of watts.
If it's a charger, it will be the number of amps.
Obviously, a combo will include both.
What is the rating in amps (amp = a) that it can handle from shore power? Generally it will be 30a or 50a.
These details will help others provide you with better feedback.
Per videos, I would watch one on each individual aspect of the electrical system, versus one that covers it all.
Remember how you eat a steak, on bite at a time.
I'd search on YouTube for:
Basic Inverter RV
Basic Charger RV
Basic Battery RV
Basic Shore Power RV
These searches should give you good introductions about each element of the system. Generally, they will include a bit about one or more of the other three, because they are all integrated as part of an electrical system.
The basics are these.
Inverter - Takes 12v DC from the batteries and "inverts" it into 120v AC.
Charger - Takes shore power, 30a, 50a or generator AC and charges your batteries.
Battery - https://www.solar-electric.com/learn...-systems.html/
Shore - 30a is for basic AC items, like microwave, A/C (air conditioning), etc. 50a is for bigger rigs that may be running two A/C units, big screen t.v., microwave, etc. all at the same time.
Generators - They need to be quiet so as to not disturb your camping neighbors. Imagine how wonderful it would be if all the campers were running noisy generators in the peaceful outdoors.
They need to be able to run, in general, the same items you would run if connected directly to shore power, but maybe only one or two at a time.
Finally, the type of electricity they use matters. A regular generator makes AC, but it may not be clean enough for sensitive electronics, like computers, to run on. Inverter Generators make AC power, converts it to DC and inverts it back to very clean AC. Some say it's cleaner than the AC that is supplied by the grid.
Research and understand each of these components individually, they will cross over as you learn and pretty soon you'll be putting the pieces together.
Best of luck.