Navigate to the high level Application which contains the calendar (likely RECORDS) and click the Calendars dropdown on sidebar menu. Select the calendar you'd like to use.

This is the default view of the calendar - it typically starts on the Month setting focused on todays date.

Multiple day events are shown as spans across multiple days. Colors are automatically determined by the name of the schema. Clicking on the event will open the event record so that it can be edited and adjusted. New buttons on the top right are available for each schema added to the calendar. Clicking on Week, Day, or Agenda will show different alternative views of the same information.