Click Account Settings, and then click Delegate Access.
Search for the person’s name in the address book.
Click Add and OK.
Selected the Permission you would like to give the user.
What are the delegate permission levels?
Reviewer With this permission, the delegate can read items in your folders.
Author With this permission, the delegate can read and create items, and change and delete items that he or she creates. For example, a delegate can create task requests and meeting requests directly in your Task or Calendar folder and then send the item on your behalf.
Editor With this permission, the delegate can do everything that an Author has permission to do and additionally can change and delete the items that you created.