On your calendar in Outlook, you can right click on the left "Calendar" (your calendar) and click "Sharing Permissions".
Next, you can click "add" and find the person in the directory.
Then grant them the level of permissions needed.
Finally, that person can add you to their calendar list by going to Outlook ribbon and clicking "Add"-> "From Address Book".
If you would like to delegate access to your account, there is a separate way to do that yourself.
Open Outlook and click on "File" menu option at the top. Find and click on "Account Settings" and then "Delegate Access"
Click "Add". Find their name again from the directory, click Add and Ok. Then you will see options for Calendar delegate access.
