This project is a simple example of Firebase being used as a Realtime Database using Android. For more information on Firebase please visit the Official Site.
Firebase realtime database is a schemaless database in which the data is stored in JSON format. Basically the entire database is a big JSON tree with multiple nodes.
After you download the project you would need to register the project with Firebase, it will generate a google-services.json file which you need to include in your project.
Go to the Firebase Console to register you project. You will need to create a google account if you don't already have one.
Once on the Firebase Console, go ahead and click on Create Project and enter your project Name.
Once created, you will be sent to a Get Started Here page and select Add Firebase to you Android App
Include the Android package name for the optional boxes you can leave blank.
Download the google-services.json file and include it in your project's app directory.
Follow the instructions to add the correct dependencies to you project (This project will already have the dependencies, therefore you can skip this step).
To see your database click on the hamburger icon on the top left corner and select Database and select Get Started for the Realtime Database.
Right now, you database contains nothing. Run the Simple Firebase Application in Android Studio and create a user.
You should see the entry in you Firebase database.
This Simple Firebase project you be enough to get you started.