To learn Android programming in Kotlin, start with the TimeFighter tutorial.
After that, choose the thing you next need to learn.
Learn more about the Kotlin language.
Learn to add a new activity (page) to your app.
Learn to save data – Preference data (key-value pairs)
Learn to save data in files (just for your app)
Learn to save data in the cloud using Google Firebase (more advanced)
Don’t see it here? Look in this big pile of tutorials