Reminders - or Alarms - can be keyed to a location or a date/time. For example, you can set a Reminder telling you to pick up the dry-cleaning when you get into town. The Reminder will pop up as soon as you reach the Location you define. Or you can set a time-based reminder, for example to remind you to watch a TV program.
In both cases, any Note you've written can become a Reminder. Write a new Note, or find an old one and click Edit. You'll see two buttons at the bottom of the screen; one to save the Note in the regular way and the other to save and also make it a Reminder.
When you save a Reminder you'll be asked whether to set it up to trigger on Location or on Date/Time. So click whichever it is you want and select either the Location name or the date and time.
When the reminder triggers an alert sound will play and you'll see a message in the status bar. The alarm continues to sound every five minutes until you acknowlege the reminder by reading the Note.
When you open Memabilia the Notifications button will be clickable and will take you to the Note corresponding to the Notification. If more than one Notification has fired you'll see the Notes for all of them. The status bar message will disappear and the alarm will stop sounding.