Your first picture is the battery disconnect switch. It clicks when you press the button near your door to isolate your batteries.
The second picture shows your
12v bus bar, where a bunch of
12v connections are made for your lights, etc.
The 3rd picture of the black box is where your trailer lights and brakes are wired.
Without an inverter, no outlets will have juice if you are not plugged into shore power. If you are not plugged in only
12v items will function, such as your lights.
No inverter = no microwave, no TV, etc when you are not plugged in.