Desktop Outlook

• Switch to calendar view
  
• On the ribbon at the top of the Outlook Window click on Share Calendar
  
• Click on the calendar you with to share.  For most users there will only be one entry called "Calendar", however if you have multiple calendars they will be shown here and you should choose the one you'd like to share.
  
• The properties for the selected calendar will open with the Permissions tab selected.  Click on Add...
  
• Now select the user that you'd like to share with from the Global Address List, then click Add and OK
  
  
• In the permissions area, select "Can view titles and locations", "Can view all details", or "Can edit" as appropriate (Delegate is a valid option, but is better managed in a different area), then click OK
  
  
  
• The person you shared with will then receive a notification that your calendar was shared with them.  They just click the "Accept" button in the toolbar of the message to add the calendar to their calendars view