Go to Calendar add-on → Add Calendar → Create new

In the opened dialogue enter the name of the calendar, select one of three possible conditions for issues to be displayed (project, JQL, Filter), cards' and text colours. After the creation, you can customize it according to your needs. 

Display modeDescription
ProjectSelect a project from the dropdown list below. The issues will be displayed in the calendar only from this project.
Saved filtersSelect a saved filter from the dropdown list below. These are saved filters that users created in JIRA issues search. Only issues from the filter search results can be added and displayed in the calendar.
JQL (Advanced)Type in a JQL in the field below. Only issues according to the JQL results can be added and displayed in the calendar.

Notice that the issues will be displayed in the calendar to the users accordingly to the user's permission.

Layout configuration

Users can customize the Layout (default calendar model, shown time and other), also can choose or create any date and time fields which would be associated with this particular calendar as a start and finish dates and time for events. 

Users can add additional fields to issue preview cards and issue cards on a calendar view to highlight essential information.