You can set reminders to yourself via the attachment type called Note. Depending on how you have enabled it in Settings->User Profile, a reminder will pop up on your mobile device or be emailed to you at a selected date and time.
To set a reminder, click on the Note button under Attachments for any item.
You can directly set the date and time or specify how many days, weeks, months, or years before the reminder is sent. You can even set repeat reminders per day, day of week, day of month or annually over a customizeable timeperiod.
When there are multiple system users, the reminder will be sent to the user who created the note and reminder.