As part of your organization setup, you will add managed users and define groups of those users.
Managed Users
A managed user is a Box account that you directly control through your Admin Console; think of a managed user as one of your employees for whom you can control and curate nearly every part of their Box experience. As an Admin, you can edit, delete, enforce security settings, and run activity reports on these users. Any content that these users upload into folders they own (or, in other words, have created) will count against their individual storage allocation.
See Adding Managed Users for details.
Other types of users are external users and unmanaged users.
External Users
Adding business partners, customers, or consultants to your Box account does not require taking action in the Admin Console. You can simply add them as collaborators to a folder. Box recognizes that these individuals are not among your managed users, and adds them to the external user list for you to track in the Admin Console. Additionally, Box displays a small globe icon next to the name of each external user.
Unmanaged Users
Unmanaged users are people who are part of your organization but are using unlicensed Box accounts, possibly because they signed up for an account on their own, or already had one, outside of your organization. Unmanaged users may or may not also be external users, but they also represent a potential security risk, as they are not subject to your organization's Box security and compliance policies. Run a User Details report to identify your unmanaged users.
Groups
On Business Plus and Enterprise plans, Groups enable you to add multiple users to your folders and decide what permissions they’ll have in those folders. See Creating and Managing Groups for details.