You will need an App ID API key from Facebook in order to use this block. It is very simple to get one, and you'll obviously need a Facebook account.

To get a developer key, please visit https://developers.facebook.com/
Note: This guide was written on 5/8/2015, Facebook changes rapidly so things might be slgihtly different.

Step 1:

1. In the top toolbar, click "My Apps" and click "Add New App".
2. When it asks you what your app will be used for, select "WWW - Website" then choose a new name for your app.
3. Be sure to choose "no" when it asks you if it's a development version of another app.
4. Finally, choose a category your website falls under. This doesn't affect the app, but mostly for Facebook.
5. Click "Create App ID"
6. Facebook will drop you into a "Quick Start" area, please skip this step by clicking "Skip Quick Start" in the top right corner.

Step 2:

1. Once out of the quick start area, you'll be dumped into your App's main dashboard page. Right now, you CAN'T just use your App ID! You need to fill out some information.
2. On the left sidebar, click "Settings"
3. Fill out the Website URL and Mobile Website URL
4. Save Changes

Step 3:

1. Copy your App ID into the block's settigs area in Concrete5
2. Adjust other block settings as desired and hit "Add!"
3. You should now have a working Facebook comments section.