Your business may have events on top of the regular rostered shifts, in which case the events feature can come in very handy.
Enabling events
Events are not enabled by default. Go to Settings > Events:

Check Enable forecasts & events and click save:

Go to the Roster view, and you will see the Events & Forecasts row in your table:

Adding events
Expand the Events & Forecasts tab and double click on the cell of the day you want to add an event to:

Enter the event details and click save:

Now you can assign shifts for the event, or assign and offer shifts.