Difference between unity basic and unity android

I have developed some simple android apps but never games. I want to develop 3d apps and games for android. My question is why do we need unity android ? Is it required to develop the app or it is just for porting the app to android ? Actually, I do not have unity android as it is paid. Is it possible that I first develop the app using unity basic . Once the app is made and I am convinced that I can make it, then I buy unity android and port it. Is this possible ? Any help to understand purpose of both modules(unity basic and unity android) will be deeply appreciated.
Thanks,
Noob

Unity Android is required at least for the final build step to get your game on Android.
It is possible to build your app with the Basic licence first and then adjust it for Android. However, you might hit some obstacles afterwards which would have been better tackled at the beginning of the implementation.
But as you are starting with Unity development it certainly makes sense to first get acquainted and then buy your Android licenceā€¦