Android APK installing method
In Android versions &lt;= 4.4 (KitKat and older) the APK file is simply copied into /data/app folder, a cache file is generated for it and installed on the cache partition. When Android is booting, it checks if cache files for any APKs are missing and generates them if necessary. And that's it.

In newer Android versions (>= 5.0 so Lollipop and newer) it's a bit more complicated because of the new ART virtual machine. A new folder is created in /data/app for every app and the APK is placed there. Libraries are extracted from APK into /data/app/&lt;app_folder&gt;/lib and code is piped through ART's ahead-of-time compiler. That's why installing apps takes much longer in ART-based Androids.

Other files aren't extracted from the APK unless the app itself does it.