As a calendar admin, you can create a sub-calendar for someone. This creates a scheduling space for that individual.
You also need to add that individual as a calendar user. This is how you grant access to the sub-calendar you've created as their scheduling space.
So you might have a sub-calendar named Bob Smith, and a calendar user named Bob Smith. While they have the same name, they are two separate things:
The Bob Smith sub-calendar contains the events (the data) for or related to Bob Smith; these events might be created by the user Bob Smith, or added by someone else (e.g. a supervisor or colleague).
The Bob Smith calendar user can view and work with the events on that sub-calendar; he might also be able to view events on other sub-calendars, depending on how his access has been customized.