Your RV lamps and other things use 12 Volts DC (See Electricity). Household appliances use 120V AC. You must have both available in the RV: they are not interchangeable.
The RV comes with a built-in 120V->12V converter. If you have park power, then your 120V and your 12V are both taken care of.
See my notes under Setup for some other considerations here. For example, the converter charges your batteries. If you are on park power for an extended period, you can fry your batteries.
Your RV may have a generator or you may wish to purchase one. A generator replaces Park Power with many of the same considerations as park power except you use your own gasoline.
This is 12V. If you wish to run household appliances with battery power, you need an inverter. The batteries that come with the RV will hold you for one or two days. If you need a longer time, you will need more or bigger batteries. There are Web Sites that give serious discussion on battery requirements.
If you are boondocking and need serious battery power, you will want to make sure that you can recharge them with a generator or solar power.
Solar panels charge your batteries in a manner similar to the engine alternator. The difference is that the alternator charges when the engine is running and the solar panel charges when the sun is shining
Solar power is becoming more popular as the price descends. Boondocking is becoming more popular as the park prices increase. If you live in the Southwest and you ever plan to stay outside of a park, you should seriously consider solar power.
If you have solar power and need 110vac, you need an inverter. The more power, the bigger the inverter. The bigger the inverter, the more drain on your batteries. The more drain on your batteries, the bigger the solar panels, the more batteries you need, and the larger the wires from the battery to the inverter.
Solar is totally silent and you may use it in places that restrict your generator. Most park rules on use of generators are absurd. This is because generators historically have made too much noise and the people who used them seemed unaware of the noise. New generators are much quieter but the parks will not be changing their rules.
Wind power is available and operates similar to solar. The visible difference is that a solar panel inconspicuously sits on your roof and a windmill cannot be hidden.