The last section on the Calendar interface is the Shared Calendar panel.
Any address may be provided here, and if the owner of the address has allowed the user to see their Calendar, then their Calendar will be shown here.
Example:
Two users: JohnDoe@merakdemo.com and merak@merakdemo.com
JohnDoe@merakdemo.com filled in merak@merakdemo.com address to Friends and set the Sharing Settings option in Calendar Settings to Friends or to Public & Friends.
merak@merakdemo.com user logged into WebMail and filled in JohnDoe@merakdemo.com to the Shared Calendars field. After clicking on View button the Calendar of JohnDoe@merakdemo.com account will be displayed.
For more examples and a better understanding of Sharing for Calendars and Contacts see Sharing Concept
The Shared Calendars panel may be changed in the Calendar Settings, so often-used addresses can be pre-defined in a window:
The first item is always the address of the current user. The others are the addresses which are filled in Calendar Settings -- Shared Calendars. The User may simply change the shown Calendar by clicking on appropriate address.