For step by step on creating reminders, click this button Reminder How To
To create a onetime reminder:
Select One-time Category (or template), or whatever name was given in the /Settings/Template tab.
Enter Reminder name (required field). Subtitle is an optional field.
Select Date and Time by touching the date and time fields. Click Preview Changes when done, then follow insturctions.
Click on the Reminders link, on the top left corner.
Now you have the reminder you created listed in the Reminders List.