To go https://developers.facebook.com/apps? and click the +Add a New App button. Enter in your website name for the display name, enter in your email address and click Create App ID.
Next click Set Up under Facebook Login.
Select Web on the next page.
Next screen Tell Us about Your Website, enter in your URL in the Site URL section and click save.
At this point just click Settings in the left menu under Facebook Login. Under Valid OAuth Redirect URIs you will need to enter in the URL to the facebook code in Sytist.
This is going to be:
If your Sytist is installed in the root of your website (your main website), it will be: https://www.yourwebsite.com/sy-inc/facebook/index.php
If your Sytist is installed in a sub folder on your website, it will be https://http://www.yourwebsite.com/folder-name/sy-inc/facebook/index.php
You will replace yourwebsite with your domain name and folder-name with the name of the folder your Sytist is installed in.
Click Save after entering in that info.
Next click Basic under Settings in the left menu.
In the App Domains section, enter in your domain name with the www. and without the www. Example: yourwebsite.com and www.yourwebsite.com
Next at the top of the page next to Status click the OFF button.
In the Make App Public dialog, under category select Business and Pages and click Confirm.
Now your can get your App ID and App Secret which you will enter in Settings -> Facebook & Share in your Sytist admin.