Who are Superusers? - Superusers are regular users that have added ability manage all: users, tests, lessons, programs and change any setting in your site. Like regular users, Superusers can take tests and have access to all the system menus that a regular user can access. In addition, Superusers have access to additional "Manage" menu that lets them manage and make any change in your site.
It's very important to limit the number of Superusers to a small number of trusted individuals.
Regular users are managed and added under the Manage - Users menu. Since Superusers are a superset of your Regular users, they can also be edited under the Manage - Users menu (see where you Edit a User's Access and Security Information). For example, you make a regular user a Superuser where you Edit a User's Access and Security Information.
You can optionally give Regular users the ability to manage limited groups of users, tests, and results using the User Security Group features. Go to Manage > Settings > Configuration and choose User Security Groups to learn more.