With the Calendar app, you can see several calendars—including your work calendars—all at the same time, all in one place. To use Calendar, you'll need to sign in to your PC or the app with a Microsoft account. When you open Calendar, you'll see all events from your Microsoft account. To see events from other calendars, add the accounts to the Calendar app.
Because of changes Facebook has made to its software, Facebook integration in Calendar is no longer supported. This means that Calendar will no longer be able to get info from or share directly to Facebook. For more info, see Facebook Connect is no longer available.
As of January 30, 2013, Google stopped supporting new EAS (Exchange ActiveSync) connections in some scenarios. This means you can no longer add or sync your Google calendar but you can see your events by moving them to Outlook.com.
If you change your time zone, you'll have to close the Calendar app and reopen it for the changes to take effect. To close the app, drag the app to the bottom of the screen, and hold it there until the app flips over.
Here are some instructions to help you get started using Calendar.