The Facebook Open Graph tags are a way to describe your page to Facebook. When utilized, you can easily control the title, description, image, and other information that is shown in a user's wall when a page is Liked, Shared, or Commented on. This helps to ensure that the message and brand for your pages is always how you want it to be.
The Open Graph protocol is how you describe pages from your site to Facebook. Set the title, description, image and more that will be used in Facebook feed entries.
Once the description tags are setup, you can start automatically posting to a user's Activity Log on Facebook when a user reads an article, joins a group, uploads a photo or performs other 'actions on your site.