Multiple navigation widgets

Little bit beginner question, but I fail to figure it out.
I am trying to have both BottomNavigationBar and a AppBar with a couple of navigation buttons.
However I only manage to run one at a time and not both. I want to have them on different files and call initialize them in main.dart, to keep it clean.

So my question is, how can I run multiple navigation bars at the same time? What should i include in my code? Especially if i want to use my home: to boot in login screen.