In general a role represents the role of a user and every user is assigned to a specific role. If you create a new user the assigned scopes from the role are copied to the user. This means also if you change the assigned scopes at the role later on this has only an effect for new created user. To change the assigned scopes for existing users you need to modify the user directly.
Besides the scopes every role has also an assigned category. A user sees and creates only resources under this specific category. By default you can simply use the "default" category.