Set up a dashboard (or several), then add a school calendar.
Edit the dashboard so that it contains the information you'd like.
Firefly comes with one dashboard but it is possible to set up different dashboards for different groups of users, e.g. one each for students, parents, and teachers.
Firefly supports integration with calendars from Microsoft's Office 365 Cloud service. This means you can display your Office 365 calendar in Firefly as you would any other calendar.
Add a Google, Yahoo! or iCal Calendar so that students, teachers or parents can view what's on in the coming days or weeks.