Porting an application from one Android version to another. Is it possible?

Question

Mobile development

Hello. So, I'm wondering if it's possible to rewrite the application from one android, for example from 6, to a smaller version, for example 4. A lot of code will have to be rewritten and are there any manuals about this? I'm a total noob in programming. I don't know a damn thing, but I'm going there anyway. You have to start somewhere. So please write in plain language

Answer 1

Yes, you can. But not always.
Manuals for rewriting code? Seriously?