Your site can have Facebook, Twitter, and RSS Feed displays as seen at the bottom of this page. These are just examples of the features, the actual linked to content can be from any source that makes it available.
For Facebook, just about any Facebook account that makes their postings available to the general public.
For Twitter, you might have to setup the feed on your own Twitter account and then use the Twitter ID and Username in that widget.
For the RSS Feed, the source can be from any website that has an RSS Feed available for the general public.