Integration with external calendars can be accessed from Team View
Export Team view to external calendars pop-up window on Team View
or from Employee Calendar
Export absences to external calendars pop-up window on Calendar
Click on the icon to go to My Feed page. There you can choose which feed you want to share with external calendars: My Calendar, Team View or Customisable feed. With the later you can choose what departments to include in the feed.
My feeds screenshot with fields to select  type of data to export