How to do to in Primavera to navigate between the tree major windows: Projets / Structures and Activ

Hi Gurus

I start with Primavera. I used to work with Oracle PJT before.

I have one fundamental question with Primavera Prof. P8.

I understand the differences between Project / Structure and Activity.

But :

1/ I don't understand the navigation. Because how can you be sure that when you create an activity,this one is linked to good level of the structure.

2/ And how can you change of view between Projet / Structure / Activity

Thanks for your answsers

Thierry