How are Android applications (Facebook etc.) installed to an android phone?

I know how to install an application to an Android device e.g from Play-Store or via an .apk file. But I'd like to understand the actual process of installation.

E.g. on Windows:

• Serial codes etc. are placed in the registry
• Files important to the running of the software are placed within the Program Files folder (the main .exe etc.)

So far, what I do know about the Android application installation process is:

• After an android application has been executed, data freshly downloaded are placed in locations like: Android/data or Android/obb etc.

• If specifically expressed by an Android developer, files can also be placed elsewhere e.g. on secondary storage (memory cards, cloud storage etc.)

But other than that, my knowledge concerning the Android installation process is pretty slim e.g.:

• I don't know where important files relating to an Android program's execution are placed (in the case of Windows, the .exe, related media, libraries etc.)

• I similarly don't know how these files are structured, after installation of an Android application e.g. *are they set out in java, res, menu, layout folders etc. as in the case of their development within development environments like Android Studio?

• Neither do I know how these files are stored upon a user's device (after being unpacked from the downloaded android installation file or apk) e.g. are they stored as .java and or .xml files as in the development environment etc.

Hopefully someone can fill in the blanks, thank you.