To set up your Facebook comments either go to the Blog Settings button at the bottom of your blog or go to the Settings tab and choose Blog.
Now, scroll down to the Comments section and pick “Facebook” from the Commenting System drop down menu.
Once you've made this selection, you'll need to enter the Facebook URL for either your personal page or fan page so that you can moderate your comments.
If you're not sure what this URL is, just go to your Facebook page and copy everything that follows the "facebook.com" portion of the address.
Save your changes, Publish your site, and you're all done. Your blog is now using Facebook for comments!
And when anyone comments on your blog post they can immediately post their comment on their own Facebook account or Fan Page, which will lead their followers back to your site.
Take that copy and pasting!
Maybe you don’t want any comments on your blog posts, no problem. In the Blog Settings, switch Comment visibility from Show to Hide and save. Any posts after you make that change will no longer show comments.