Here are the step by step instructions for getting your Facebook AppId.
First thing to do is to ensure you are logged in to the Facebook acount you want to be the owner of your App.
Now you can go to the Facebook step by step process Facebook Help Guide
Things to remember:
Then you're all set to go!
Your Facebook App should start in development mode. This means that posts to Facebook are only visible to approved developers of your app. So, you can test the Facebook posting without posting to your timeline where everyone can see.
You can add other people to your app developers group, and then see how the Facebook posts look.
When you’re ready you can turn on live mode in the facebook developer app page -> App Review. Just flip the switch at the top of the page. The Facebook interface does not use any permissions that require you to go through an approval process, so it should just turn live on automatically.