To create a Facebook App, go and visit: http://developers.facebook.com/
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. On Facebook Developers page, click on "My Apps" at the top right hand side of that page and login to Facebook if you haven't done already. If you're on the App page click on "Add a New App" at the top right hand side. A new window will pop up (see image below).
You must have to enter canvas URL and site URL to post on facebook. For Add Url go to "Settings" > "+ Add Platform". It will popup a window as below image. In that Add "Facebook Canvas" and "Website".
once you click on "Facebook Canvas" and "Website" you will see the page as mentioned in the image below :
Within the Application Info make sure, that you enter the correct URL of your "Site URL" and "Canvas 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.
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:
Now, Click on the Dashboard menu and copy and paste the App ID and App Secret Key as below image:
Important: When you copy and paste all the needed IDs and Keys, make sure, that you don't have any empty spaces, either at the beginning nor at the end of these entries. If you have any empty spaces, then the Application won't work and will show an error message when you try to connect to the App. Click on "Save Changes".
Note: Below section is only for Social Auto Poster plugin
Update - May 2014: Facebook changed some rules regarding the apps. This means that the Facebook App, Facebook profile or page and the user who authorizes the app MUST belong to the same Facebook account. So please make sure you are logged to Facebook as the same user who created the app.
Important: When Facebook Authorization Wizard asks you for the access privileges to your profile/pages, do not uncheck anything and don't click "Skip".
Facebook don't have the ability to request permission to just one page. It's either all of them or none. If you click "Skip" it means you forbid Facebook from posting to any of your pages, groups or profiles. Our plugin will post only to the page that you specify on the "Your Facebook URL" field.