Here is an awesome guide by one of our members : https://premium.wpmudev.org/forums/topic/guide-updated-ultimate-facebook-plugin-for-2014
Just to keep the steps upto date, I created a new thread so that I can tell you how to create a Facebook App, please be sure to log into Facebook.com
This *should* automatically log you into the developer portal. You will have to provide your password and set permissions.
Step 1: Visit https://developers.facebook.com click on Apps and you will see the option to “Create New App” click it
Step 2: Name your App. Doesn’t matter what you name it, Facebook will give you a “Valid” or “Failed” notice next to the box after finish typing it.
Step 3: Complete the App. See the pictures below. These are the only fields you need to complete.
Make sure you set the Sandbox Mode to Disabled and save changes
Then, simply transfer your API information to whichever Plugin you are using and check that it all connects.
Please Note: You should only have to do this ONCE per site. You will not need to recreate or re-use this API information on any other plugins. All WPMU DEV plugins come with a built in checkbox where you can specify that you are using the Facebook API already via another plugin. Calling the API multiple times on the same site can create problems.