To create new reminder enter the issue and click on 'Reminder' button:
Select a date and time, the message is optional.
You can use 'Tonight', 'Tomorrow', 'In a week', 'In month' to create quick reminders without messages.
'In a week' adds 7 days to current date and time, 'In month' adds 1 month, the time stays the same as current moment.
'Tonight' and 'Tomorrow' time are configured in Reminders Settings menu under your avatar (Morning time for tomorrow and Evening time for tonight):
'My Reminders' menu under your avatar shows you all reminders created by you.
You can remove reminders by clicking on the cog button.
If you are JIRA administrator you can see all users reminders in Reminders administration menu:
Administrator can remove reminders by clicking on the cog button.