Supasite's User Management features allow multiple people to work on the site. By default, they are stored in the database, and are authenticated each time the admin script is run. With [include_path]/auth_cookies.php (the default authorization method), the script checks for a cookie. If one is not found, it prompts you for your username and password. From there, it checks it against the database and either grants or denies access. If a cookie is found, it takes the data and authenticates that against the database as well.
When you create a user, you can assign one of three privilege levels: