To create a Facebook App, go and visit: http://developers.facebook.com/

Facebook Developer Page

Note: You need to use a personal Facebook Account for creating an App. A business account won’t work. Your personal account needs to be a verified Facebook account. If your account isn’t verified yet, you’ll receive a text message from Facebook to verify your account. So make sure, that you have a mobile number set within your account, otherwise you won’t be able to create an App.

Create A New Facebook Application

After enter all field click “Create App ID”. It will popup a window of Security Check shown image below, click on Submit.

Facebook App Captcha

Now you have successfully created a Facebook Application and you should be redirected to the “+ Add Product” page which should look like the one on the image below:

Facebook Product Page

Click on “Set Up” button of the product Facebook Login, after that you will see the page as mentioned in the image below.

Facebook Select Platform

once you click on “Web” you will see the page as mentioned in the image below :

Facebook Canvas URL

You must have to enter site URL to post on Facebook, after that click on menu Settings->Basic as mentioned in image below:

Facebook Canvas URL

Within the Application Info make sure, that you enter the correct URL of your “Site URL” and the URL does match 100% the one from your website. So if the URL of your website does include the www like http://www.domain.com than you need to enter it like that. If the URL of your website doesn’t include the www, than you don’t need to include the www within the URL. It’s important that the entered Website URL does match the one from your actual website, otherwise the App won’t work correctly and it will show an error message when you or your users try to connect with the App. After adding Site URL, Go to Facebook Login settings.

Click on “Settings” as shown. After clicking on “Settings”, you will see page as mentioned in image below :

Facebook Social Login Product

Within the product settings, make sure that you enter the correct URL of your “Valid OAuth redirect URIs and “Deauthorize Callback URL” and the URL does match 100% the one from your website. So if the URL of your website does include the www like http://www.domain.com than you need to enter it like that. If the URL of your website doesn’t include the www, than you don’t need to include the www within the URL.

If you want to use your own Logo or image for the Application, you can do that by clicking on the “Settings” > “App Icon”. After clicking on “App Icon”, you’ll get open popup. Click on the “Choose File” and upload your custom image for the App. We recommend that you’re using a custom image for your App. This will give more trust and does look more professional when a user does connect with your Facebook Application. See Image Below:

Facebook Change Icon

Note: Your newly created Facebook Application will be in Sandbox Mode as default. To get the App Live, click on App Review > “Make Your Application Name public?” . See Image Below:

Facebook App In Spam Mode

Select Yes it will popup a window as shown in the image below. Click confirm to get app live.

Facebook App In Live Mode

Now, Click on the Dashboard menu and copy and paste the App ID and App Secret Key as below image:

Facebook API Key & App Secrets

Source: http://wpweb.co.in/documents/social-network-integration/facebook/