Each Matter has its own email address.  You can view the email address in the Matter’s Dashboard in the “Matter Details” Tile.  Clicking on the email will copy it to your clipboard. 

When you want to add an event to a Matter’s Calendar, you create the Event in your Outlook Calendar as you would for any other event, and simply invite the Matter to the event by adding the Matter’s email to the list of attendees and clicking “Send”. 

In Outlook Online, it looks like this: 

In the Outlook for desktop, it will look like this: 

First you click on “Invite Attendees”, 

Then you add the Matter’s email address to the “required list”: