Users and roles

Add people in Users. Each user has a role and, optionally, a list of stores. A user with a store list only sees those stores.

Area	Owner	Manager	Staff
Dashboard, Orders	Yes	Yes	Yes
Products, Categories, Reviews, Coupons, Customers, Blog	Yes	Yes	No
Reports, Marketing	Yes	Yes	No
Appearance, Content, Settings	Yes	Yes	No
Stores, Users	Yes	No	No

Owner with access to all stores (no stores ticked): full access. Only this kind of owner can create, edit or delete owners, create or delete stores, and change the default store. The last one cannot be demoted, limited or deleted.
Owner limited to some stores: can only manage managers and staff inside their own stores, and can only give out their own stores. They cannot change their own role or stores.
Changes take effect at once: when you change a user's password, role or stores, or delete the user, that user is signed out everywhere.
On the public live demo, the shared demo owner's email, password, role and stores are locked. Your own install has no such lock.