android app. Activity, Fragments, Navigation?

Question

Android

Good day.
I began to study the development of Android applications and the questions arise:
1) In what cases should you use Activity, and in which Fragment, provided that the application is focused on phones and development for tablets is not going on?
2) How correct would it be to create one Activity with several Fragments for an "online store" type application?
3) Is there an alternative to the Bottom Navigation View component for navigating between "screens"?
4) Should I use the Navigation Architecture Component ?

Answer 1

Activities should be considered as the entry point (main) to the application. All other transitions within the application must be done on fragments or their analogues. This is true for any application.
The question about the Bottom Navigation View is not clear. It either suits you or it doesn't. It is possible to do similar behavior without it. You can use Navigation Drawer. Depends on the task.
My opinion is no, Navigation Architecture Component should not be used.