How do I add an Outlook Calendar to Calendah?

For adding a calendar as a Calendah Calendar, go to your Outlook calendar, click on Settings. Go to Shared calendars and find the ICS address, copy the URL: 

Then go to your Calendah -> Calendars and click Add:

Next, select External (.ics), and pick Outlook. Paste the secret address into File URL and click Validate: 

Done! You can adjust the rest of the settings of your calendar as needed, adding or changing properties you want to show up on a card label and card description, your sharing settings etc.