If you wish to connect Calendar to your Outplay account you can do that on the "Calendar" Tab under settings.
Click on "Connect with Google Calendar" if you wish to connect your Gmail Calendar. You can also create sub-calendars in your Gmail Calendar Settings which will also be visible to switch between once connected. Eg: firstname.lastname@example.org and New as sub Calendar that I have added as per the below screenshot!
Same way you can also connect to your office 365 Calendar by clicking on the "Connect with Office 365 Calendar" under Calendar Tab and by proving the credentials to connect.