A notebook is a container for notes, and it is where sharing is decided. You invite people into a notebook rather than into individual notes, and they hold a role in it that you can change or remove later.

Notebooks hold folders, and a folder can be kept back from some members, so one shared notebook can still have parts not everyone sees.

A notebook belonging to an organisation behaves differently from a personal one — which is why a single note inside an organisation notebook cannot always be shared on its own.