Touch an event to view its details.
If no reminder is set, touch Add reminder to automatically add a reminder for 10 minutes before the event.
If a reminder is already set, touch Add reminder to set more reminders for the event.
In the dialog box that opens, touch the length of time before the event that you want to be reminded of it.
When the time comes, you receive a notification about the event.
You can use Google Calendar on the web to configure additional reminder settings.