Refer to the facebook documentation.
Or you can use our integrated Social Networking Links, via the "Design" menu, then "Supersize my Website" then select a location to put the social networking icons or links. Alternatively, add the appropriate [SOCIALICONS] field to your template. To load up your social networking usernames, you can do this in the contact us page of your website. Please note that to get a facebook username, that you need at least 25 likes already. refer www.facebook.com/username
Or you can install a toolbar from http://www.wibiya.com/ and follow their directions, then paste this into your website template using INSERT... SCRIPT/HTML option.