After addon's installation automatically would be created 2 custom fields Start and Finish on a base of them would be available to plan issues in a calendar. Once you've filled in these fields issue would be shown in a calendar, you can do it from the calendar or issue.
You can replan issue by editing values directly in the issue or shift it in a calendar.
Calendar's administration can be reached by going to JIRA administrator menu Jira settings / Apps/ Teamlead / Calendar. You can choose other time and date fields in order to show issues in a calendar. While you create a calendar you can choose or create any date and time fields which would be associated with this particular calendar.
Add Start Date / End Date custom fields to Create and Edit Issue screens, otherwise the issues will not be visible in the calendar.