One type of sub-calendar that you can use in the Calendars tool are Event sub-calendars.
Event sub-calendars are automatically created when you create a new Event. You cannot create an Event sub-calendar on its own without creating an Event, so to create one you must click on the "Events" tab in the main navigation bar and click on the "Add New Event" button. There you can select the color for the Event sub-calendar.
Also, when you assign Contacts to an Event, those people are also automatically assigned to that Event's sub-calendar and will have access to it.
To edit the name of an Event sub-calendar, you must edit the name of the Event itself. You can only delete/remove an Event sub-calendar if you archive the Event itself.