Facebook is a useful marketing tool for businesses because it allows them to reach niche groups of potential customers through existing social networks. The document recommends four steps for marketing on Facebook: 1) Create a Facebook page for the business. 2) Search for relevant terms to learn what is being said about the industry. 3) Engage with customers by listening and starting dialogues rather than just pushing content. 4) Advertise on Facebook using targeted ads and analyze detailed analytics.