Manufacturers install 12 volt only components, such as lights, and use converters and inverters to power them. If you are connected to shore power or using your generator, the converter is supplying 12 volts to your lights. Otherwise, your inverter is supplying 12 volts to your lights from your house batteries.
Your converter is really a simple device that takes 110 volt AC and turns it into 12 volt DC. They allow you to use your 12 volt appliances, fans, pumps and camper lights while you are plugged in to 110.
Most RV power converters are equipped with a battery charger to keep the RV's battery charged when connected to a 110 power source. These chargers are usually trickle chargers with a charge rate of less than 10 amps.
Inverters work the exact opposite. They change the DC power of the house batteries to AC current. Some RVs have inverters to provide AC power at times when shoreline power is not available, or when generator use is not advised. Inverters are rated in watts, from 35 to 3000 watts.
RV Power inverters are nice to have for dry camping. Generators require fuel, regular maintenance and can be very noisy. We usually dry camp to avoid noise. Inverters are quiet - not even a hum, and are virtually maintenance free!
A power inverter relies on good RV deep cycle batteries to work properly. They work well for low power appliances such as televisions, radios, computers, and for short term use of appliances such as coffee makers or microwaves.