Beginner topic: Electricity
RV systems typically have 3 power systems.
12-volt vehicle power
This power is used for turn signals, radio, and critical engine functions
12-volt house power
this power is used to power low wattage lights inside the livable space, water pumps, and small accessories. This system can be charged by solar, a charger when plugged in, a generator, or the vehicle's alternator (battery isolator should be used).
In older RV's this power is typically only available when your RV is plugged into household power, or by using a generator. Newer RV's may use an inverter and plenty of batteries to provide power when electricity is unavailable.