Please go at this url https://developers.facebook.com/apps and click on 'Add a New App'.
Note: If the link 'Add a New App' is missing, you'll have instead 'Register as a Developer'.
Register as a developer, then the creation of new app will be available.
Please note that only real personal facebook accounts have permissions to create an App. Business accounts can't manage facebook Apps.
Enter 'Display Name' and click 'Create App ID'.
Enter the required captcha challenge.
Skip the 'Select a Product' part, it's not needed.
Once on the basic settings of your new app:
For the field 'App Domains' enter your blog domain name (example: mydomain.com)
For the field 'Contact Email' enter your email
Click 'Add Platform'.
In the field 'Site URL' enter your blog url. (example: http://mydomain.com)
Leave everything else by default.
Make your App Live by browsing to 'App Review'.
Click the rectangle indicated in red.
Go back to the basic settings of your new app.
Copy your 'App ID' and 'App Secret' and configure your facebook account in MicroblogPoster's social accounts section.
MicroblogPoster will provide you a link, follow that link and authorize your App posting on your behalf.
Disregard this alert since you're the App Admin, click 'Okay'.
However, if you created your App with one facebook user and want to use it with a different facebook user this second user MUST be developer of your App.
You can add developers in your App settings, facebook users that are developers of your App have the right to post with it, just like the App admin user has.
Choose the share level.