Now click Add Action and select the Send Notification button.
4. Create the notification
On this notifications page, several types of communications can be utilized (on-screen, email, etc). There are also use several Tokens on the right side of the screen to make the notification more personal or more general. These automatically fill in information depending on the Token. For example, [[Appointment.Attendee.FullName]] will automatically become the recipient's full name when it's sent.
The text in the Body box is what the recipient will see. Feel free to use the text in the screenshot, or create a custom one.
5. Save the notification & Rule
Click the Save button on the Notification Page, and save the rule itself on the Rules page.

Be sure to save the notification on the Notification Page, and the rule on the Rules page. If both aren't saved, the notification won't work.