Sap Lumira Designer VS Lumira Discovery

Dear All,

Hope you all fine.

Can anyone please help me to understand what is the difference between Lumira Designer and Discovery?

If I understand with Discovery we can not create an application, it can be just story. So we can not write script for any event on click or onSelect....

And what is exactly the story? I mean what is the difference between story and App or report?

Any help will be appreciate

Sepide