Help with java code for an app

Question

The following link will take you to a GitHub repository:
https://github.com/Ozzy-Ochoa/Gym-Labs-App .
I am a beginner in programming and I don't know much about the subject and much less about android, but I would like some help or an introduction on how to plan my app more, tips etc.
It would be like a type of advice since I don't know much, I appreciate your help to those who are encouraged

Answer 1

App development is different from classic Software development.
You are often use System.out.println
It's better to save it in a string. So you are more flexible.
Check out Android Studio.
This can be overwhelming at the beginning. The program is very heavy. Without a tutorial your are easily lost. It has it own program structure. You can learn much about Software development if you understand how Android Studio handle your files. They separate things to get a better order of everything.
It has many smart functions and a GUI builder. So you can design your app per drag and drop.

Answer 2

This is what I'm learning from:
https://developer.android.com/kotlin/campaign/learn

And books... (yeah, I'm that old and kind of person)

Other documentation could be the kotlin docs.

Another place to start is with the Kotlin course on Sololearn, or Java.

Answer 3

I have Android Studio and I created a project in it, I even used the github code in android but I got lost and stuck, at the moment my app has a start section, registration and some menus without any information inside, "A skeleton of app" more or less.
Since I am a beginner, I don't know which database to use and how to configure them, but I am watching tutorials and learning little by little.
I would really like to have help such as: steps that I should follow, types of documentation, versions of app interfaces, things of that kind, something more theoretical or procedures, since I don't have this information since I study on my own.
Thank you very much for responding so quickly to my message Estefano.