SIMPLE and MINIMAL starting android app that connects to Google firebase real time database with email and password as login and register a new user.

A couple of years ago I had started learning to write apps with android studio, but because of medical problems I had to stop for a while. I had written an android app that connected my app to Google real time database. I could have it register a new user and add them to my firebase real time database. But that code no longer works because Google has changed some things in android studio. I want to have working code to do this again. The code that I am looking for must be in Java that will run in the current version of Android Studio. I want it so that the user just clicks on registration (or register or whatever) and then it will allow them to enter a username (their email address), their password , and their favorite number, and their favorite color. The app will allow them to log back in to ONLY their record so that they may change their info or whatever. I need to verify that the app connected to my project and the user is added to the database, or changed, etc. Since I would like to know what was changed I need you code annotated well in the app. Explain what code needs to be added to the app build.gradle file and where in the file it goes for example. When I was writing this app I did not make it overly complicated to just demonstrate funtion. I was planning to add input and error checking later. It would only take me about an hour to make this app.