Step 1: 

• Home screen > scroll down to Calendar > Tap "Create Event / Holiday"
• Tap + button on the right of bottom of Calendar screen

Step 2: Enter event name & description & location with a start date and end date, choose which type of this event.

Step 3: Press "Done" and it will publish to the office calendar and everyone ready to view.

Here is the full video of how to add a public holiday/event to Calendar.