This will depend on if you want this visible on the Public Calendar or not:
Visible: Create a new event, select the Public Vacation Calendar designated for PTO. Mark it as an All Day Event and check off Block Out. After selecting the Company Calendar, a new section will appear on the right side for you to select My Calendar.
Not Visible: Create a new event, select your Personal Calendar. Mark it as an All Day Event and Block Out.
See the Add new Out Of Office event guide for more info.