An RSS feed is a web technology used to publish frequently updated content from websites, blogs, etc.
In the case of Catholic Outpost, we are simply re-publishing the same content that is already on the website. So it's not different information, just a nifty way to access the same information.
All you do is subscribe to the feed (which is free) and it allows you to more easily stay updated on any changes to the website.
The only thing you need to subscribe to an RSS feed is a "feed reader" or "aggregator".
There are many free feed readers available.
And actually most all of the new internet browsers (like
Internet Explorer 7
and
Firefox) have them conveniently built in.
A few other popular free ones are
Bloglines,
Google Reader,
and
Newsgator.