iCalendar file (.ics) is used for calendar apps.
Import an (.ics) file into Calendar (Outlook 2010):
1. On the File menu, click Open, click Import.
2. Select Import an iCalendar (.ics),click Next.
3. Select (.ics) file, click Import.
Holiday file (.hol) is used for calendar in Outlook.
In order to use this file just download, execute and select the selections you want to add to your Calendar.