Google search ads used to account for the bulk of online advertising dollars: it was a straightforward way for campaigns to provide information about their activities to those searching for it.
Look in your account and privacy settings, and you see a lot of information on social ads and Sponsored Stories, including the possibility that you can appear in them.
The staying power of ads on Facebook is three times that on other sites, because customers stay longer on the site on account of the increasing functionality built in the platform.