Confirmation emails are sent as soon as you make the appointment.
Please note: Confirmation emails only apply to new appointments. If you are modifying an appointment, the confirmation email will not be resent.
Click on Setup, Business Info, Email tab.
Under Grooming, check the first checkbox, 'Send appointment confirmation email'.
You can enable any of the other options as needed.
The three boxes are so you can add any additional information for your clients. Examples would be if you want to include your cancellation policy or give your pickup/dropoff times.