Users are organization-specific: each organization has its own set of users.
Users can be added or modified in one or all of the following ways:
by an administrator, manually
by an administrator, importing information from a file
by a user who creates their own account (if the LMS is configured to allow this)
by users accepting an invitation to take an activity
when a user is redirected to the LMS via the optional AICC interface
through the web services interface (usually occurs when the LMS is integrated with another application or a web site)
Note: Simply creating a user account may not necessarily give that user access to learning activities. Learning activities need to be made available to users.
To ensure consistent records, individuals should have only one account, so typically you would choose to either add user accounts or allow users to create their own accounts, but not both.