Applications – How to create Android Studio and Unity Android apps with JDK and SDK

how to create Android Studio, Unity and other software Android app.
I searched the internet but did not find a satisfactory answer.
If I'm doing gameplay in Java Opengl, how can I build Apk from that? Is every program already available to convert my Java project to Android APK, or do I have to create my own?
Please help me.
Give me some resources to understand what's going on behind the scenes. How it works, how Unity and other software make a project for multiple platforms.