Though there are lot of implementations for an MVP architecture, all of them share a basic idea (or they should at least), which is separating business logic from your views (activities, fragments, dialogs). Why is that? Well, for two reasons mainly:
- separation of concerns
- Testability: your business logic is able to be tested if there is no android components involved.
About your questions:
What would be directory structure of Application in MVP?
There is no rule about that except that your MVP components should be identified. Here you have an article where I started with a package structure but then I found other more convenient.
Activity should be a Presenter or View?
Your activity (or fragment or whatever components in charge of showing view components) should be the one that implements your view.
My advice is that you should check multiples examples and see their advantages and disadvantages of each one, and try to define your own architecture from those which you will feel more comfortable with.