A Realtor is someone whose job involves helping people buy or sell a home. When people move to a new city, they'll often call a Realtor to help them find a place to live.
You can sell your house by yourself, but Realtors are experts who can advise how much it's worth, help you negotiate with buyers, and take care of advertising and marketing. You can also call Realtors real estate agents or real estate brokers — in fact, they have to belong to the National Association of Realtors to call themselves Realtors. It's tempting to pronounce this word with three syllables, but there are only two: real and tor.