Choose a Calendar
When you click on Open Calendar, you will be prompted to choose a someone from the Directory (Inside your organization) or Internet Calendar (Outside the organization).

5. Try It: Choose a Calendar
Click on From Directory.
Type the name of someone in the Directory.
Click Open

Now, Try This: Find the Calendar
Go to Home->Calendar->My Calendars.
The calendar you opened should be available under People's Calendars.

Very good.

Memo to Self: These pages show many different People. You may not be able to practice these steps if you do not have other People in your Office 365 Domain.

Home->Calendar->My Calendars-> People's Calendars