Sharing the Calendar
To share your calender with a co-worker, log into webmail right-click (or control click) a calendar and select "Sharing."
Select or type the user with whom you would like to share you calendar.
Give them the permission you would like. View, Change (make edits) or Owner.
Click "OK" and you have given permission to view or edit your calendar.
Viewing and Editing the Shared Calendar
Now the person that would like to view or edit the calendar needs to do a few things.
Log into his/her webmail, then go to the calendars and click the plus symbol.
Check off the newly available shared calendar.
The new calendar will immediately be available in webmail. It could take several minutes to appear in iCal/Apple Calendar. If you receive an invitation to join a shared calendar, accept. If you don't receive an invite and the calendar doesn't show up, restart the computer.