Processing a reminder refers to starting and completing the task. Once the task has been completed it will disappear from the reminder list, and will be recorded in the Diary. If it is a repetitive reminder, a new reminder will be automatically created in the Diary and sit there until the day it is due and then it will show in your reminders.
Click on the DASHBOARD button (on the left-hand side menu)
Click on the REMINDERS tab
Select the entries that you want to process
Click on the green arrow
Your reminders will then be processed and will be recorded in the relevant Diary.