Android Studio is the IDE (Integrated Development Environment) for the creation of Android apps and is based on IntelliJ IDEA.
I began app development with Apple years ago, but as Android has so much of the market, I have realised that it is better to start again with a different IDE, programming language and platform.
Mobile Operating System Market Share Worldwide – August 2018
Series 40: 0.23%
(Source: http://gs.statcounter.com/os-market-share/mobile/worldwide, Accessed 27 Sept 18)
So, now I am in Android development and will provide resources for app development on this site, as I work my way through the IDE.
Android Studio is found at https://developer.android.com/studio/.
IntelliJ IDEA is found at https://www.jetbrains.com/idea/.