AppFlow, how do Set Global, Assign and Set Storage work? Whats their purpose?

Still playing around with purely front end and AppFlows.

The challenge: I need a global storage, accessible from all pages with active binding, e.g. for storing state and updating on state changes (like current tab in navigation. In React, I would use a state, hook or provider.

So I played around with some steps in AppFlows and tried to understand what they are doing / how they work.

1. what is Set Global doing, and where can I access it the data?
2. With Assign, I can set local variables, I guess?
3. Set Storage, I would expect setting a session / storage global? Where would it be (what Storage?), if it would work (it throws an error on the console ‘key needs to be a string’)