Step 1: Click on File

On the Apple Menu, in the upper left corner of the computer screen, click File, then click Export.

Step 2: Select what needs to be Archived

Outlook can archive Mail, Calendar, Contacts, Tasks, Notes, and specifically categorized Items, then press Continue.
 

Step 3: Save the Archive

The .olm file can be saved anywhere on the computer for ease of access in the future.