It is often useful to have more than one Outlook calendar. The process of creating a secondary calendar is the same as that of creating an address book or mail folder—you simply create a folder designated to hold calendar items.
You can display calendars individually, or you can display more than one calendar at a time. For instance, you might have separate business and personal calendars and want to view them together.
You can view multiple calendars next to each other, or you can overlay them to display a composite view of the separate calendars. When you view and scroll multiple calendars, they all display the same date or time period.
You can drag items from one calendar to another, and copy items between calendars ...