How to Create Calendars in Mountain Lion
If you're trying to keep track of your schedule, you can't go wrong with the Calendars app in OS X Mountain Lion. To create a new calendar in Calendar, follow these steps:
Choose File→New Calendar→iCloud or On My Mac.
A new calendar named Untitled is created and added to the appropriate calendar list.
To give your calendar a name, select Untitled and type a new name.
(Optional) To color-code the entries for this calendar, first select the calendar (by clicking it); choose Edit→Get Info or press Command+I; and then select a color by clicking and holding the color swatch.
Other is the handy choice because it lets you select thousands of colors in addition to the seven colors available in the menu.
Now any item you create while this calendar is selected (in the list that pops up from the Calendars button) appears on the selected calendar in the color you selected. While you’re in the Info sheet, you can also add a description of your calendar.
The calendars appear in three sections — On My Mac, iCloud, and Subscriptions — because there are all three types of calendars on the Mac. If you are not an iCloud user, your calendars will appear in the On My Mac section instead of the iCloud section.