After selecting the "Advanced" tab in the Settings page, select the "E-mail" tab.

In the "E-mail Reminders" section of the page, select the number of days before an appointment you wish to send a reminder to your customers.

Select whether you would like to send an email to your customer when an appoinment is added or when an appointment is cancelled by checking off the appropriate box.

Don't forget to click the "Save" button at the bottom of the page to confirm your changes.