Open graph is a protocol that will help you "integrate" your website with Facebook, letting you like, comment or subscribe to an URL. For a complete list of Social Plugins you can click here. Using Facebook Insights you will see the statistics of by date and how many likes or comments you have.
I'll tell you the truth, i think i still don't know how to use it to it's full extent, but this two part "guide" can help you with the basics. This will show you how to customize the information that will be shared when you post to your Wall an URL of your website, and how to put a Like Button and Comments Box.
The first thing you need to know is that for everything to work, you'll need to use these metatags on your HEAD section of the webpage (the example used is waldou.com so you should change it accordingly:
<meta property="fb:admins" content="81...