All of these devices either convert energy from one form to another (with some loss in the process) or store energy.
A 12V battery stores energy for later use.
An inverter converts 12V DC electrical energy into 120V AC electrical energy. You need something that supplies 12V DC electrical power, which in an RV is a battery.
A converter or charger converts 120V AC electrical energy into 12V DC electrical energy. This can be used to charge a battery, or to run 12V devices.
A generator converts some sort of fuel (gasoline or diesel or propane) into 120V AC electrical energy.
A gas tank or propane tank stores energy in the form of fuel.
A solar panel converts sunlight into electrical energy. With an appropriate controller, this can be 12V DC electrical power. (Without a controller, it's rather variable depending on the light conditions and not usually all that handy for RV usage.)
To be self-contained, you need to have an appropriate supply of energy for your needs. An inverter and battery bank can certainly be an important part of that, but you do need some source of energy to "refill" the battery bank, which is commonly either a generator or a solar setup. If using the generator, of course, its power source (the fuel tank) needs to be periodically refilled too. We don't have to worry about refilling the sun, thankfully. (When traveling, the vehicle's alternator is another possibility; this is a special case of a generator that produces 12V DC power and is itself driven by the vehicle's engine.)
