Utilize the Facebook Like ButtonFirst and foremost, the "Like" button is central to Facebook's network. Ever since Facebook began littering the Internet with these buttons, it has become the easiest way to quickly share sites with your friends, far more convenient than the older, more cumbersome method of copying and pasting a link to your status update box. Businesses have caught wind of the popularity of the Like button, and have used it everywhere - on product pages and promotions, in an effort to tap into its viral marketing potential. If you have a company website, put this button everywhere - once a single user clicks it, you get free exposure to all of that user's friends, who may then spread it to others, much like Twitter's "re-tweet" function.
Create a Facebook Business PageNext, set up a Business Page. These pages can be accessed by Facebook users either through Facebook search or through a link from your company website. Business Pages can mirror your company website, in a more streamlined, social manner. Basic company and product information should be on your business page, but the page's main purpose is to provide a constant stream of information and product updates to followers. Update the page frequently, and with limited-time discounts not offered on your company website, to give users an incentive to "Like" and follow your page. Games such as raffles, after a certain amount of users have started following your page, can also be fun - award a single random follower a prize each month.
Sell on Facebook MarketplaceFacebook's often overlooked Marketplace, which functions like a socially connected version of eBay, can also be connected to your business page. If you want to open a small online store, this can be a good option - especially if you want to take advantage of the viral marketing that social networking sites can provide. Users can search Marketplace for all sorts of products, but priority is given first to the users' friends and mutual friends, who are more trusted than anonymous sellers and buyers. Results are also arranged geographically, giving it far more coverage than eBay or Amazon. In addition, Facebook's convenient messaging system is far faster than conventional online retailers, and small businesses can use PayPal instead of more expensive credit and debit card processors.
These are just some ideas to help you get started. If you're thinking of starting an online business of getting your existing one connected to the "social network", then Facebook is an excellent place to begin.