Getting started with Android

I need to port my Qt app to Android, but I can't figure out even how to get started. I've installed the SDK and the NDK from the Ubuntu repository, and I'd like to compile anything (even if it's in Java) and run it on an Android simulator, before I tackle a Qt app. The next step, according to http://doc.qt.io/qtcreator/creator-d...g-android.html , is to run

Code:

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./android update sdk

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The page doesn't say what directory to run it in, or whether I have to be root. There are several files called "android". Where do I run it?

I've managed to install Android Studio with the snap package and run a Java program on the emulator. I still don't know:
*How to install Qt5 on the emulator, or
*How to tell CMake to cross-compile for Android.