You take the client Id and client secret and put it in your .env.local file
You add the nextauth url (the localhost url in development) and the next auth secret for the jwt token in your .env.local file as well
The variables you must have are :
FACEBOOK_CLIENT_ID
FACEBOOK_CLIENT_SECRET
NEXTAUTH_URL
NEXTAUTH_SECRET
In your facebook app you must add a product, the Facebook Login
You must add this url : https://next-auth-example.vercel.app/api/auth/callback/facebookin your Facebook Login parameter under Valid OAuth redirect URIs
And you must activate for the public_profile the advanced access
In the Basic parameter of your application you must add a valid URL of Privacy Policy and of Data Deletion. You can deploy your app on vercel before adding authentication and then add the url of your app deployed in these parts.
For the Database and the storage
Create a project on firebase
Find the parameter of your project and add it to a file call firebase.js in the root folder of your app