@Courtesy goes to Difference between app-debug.apk and app-debug-unaligned.apk
The unaligned apk is just an intermediate apk. First, the unaligned
apk is generated. Then, the unaligned apk gets aligned and produces
the aligned apk which is the app-debug.apk.
Read Signing Your Applications
The build process of Android projects is handled by the Gradle build system. If you create a new project in Android studio, the Gradle build scripts are automatically created. Android studio wraps the Gradle runtime, hence no additional installation is required.
- Multi-apk: supporting the creation of multiple apk for different
device types while reusing parts of the code
Android Studio, make it easy to create several variants of an
application, either for multi-apk distribution or for different
flavors of an application. This means, you can have different builds
for debug, release or may be different variant build from the same
code.