Your organization has at least one admin. The admin has all possible privileges and can add users and change user roles.
A user can create projects and cases and can submit them. A user cannot change user roles.
A viewer is only able to view cases and results. He is not allowed to create new projects or cases and can not download or upload files.
Note that regardless of the user type, all users have access to all projects within their company. In addition, users cannot be granted access to projects from other companies.