The power inverter in a motorhome or RV uses DC power or direct current to create AC power or alternating current like it would in your home. In your motorhome the inverter is directly connected to your batteries and provides 110 volts for running appliances like your microwave, TV, computer or a coffee pot. There are many different size inverters available, from 60 watts to 5000 watts. The rating or size will be how much power can be supplied by the inverter. So here would be an example, if you were looking at powering a microwave with a 600 watt rating, then you would want to go with an inverter that was rated for 800 to 1000 watts. If you wanted to power a LCD TV which has a rating of about 150 watts for a 21 inch TV, you could use a lower power inverter of about 200 watts if that was all you were going to run.
There are two different ways an inverter can generate AC power. Pure sine wave and modified sine wave. If you will be operating appliances or other devices like a TV then the modified sine wave inverter will work fine. If you will be powering sensitive electronic gear like a printer or a microwave then the pure sine wave inverter would be the best choice.
Many inverters can also come with an automatic transfer switch and battery charger built in, but these type of inverters are very expensive and will usually end up in the mid to high level motorhomes and trailers that require a high delivery of power.
If you are interested in checking out an inverter for your motorhome, most RV repair and parts facilities should be able to accommodate you.