To get star-ratings and customer feedback from your clients, all you need to do is add the [StarRating] merge field to your "Appointment Follow Up" email (this is from the customize email/text option under the "Set up" page). 

For example you can add the text as:

"How did we do?
[StarRating]"

So what this does is when you have added the [StarRating] merge in your follow-up email, it will show up like this in the email we automatically send to your clients:

So when your customer receives the email and clicks on one of the stars, it will open up a web page for them to confirm their star rating (automatically pre-populated with the star selection they made in the email) and also ask them for any additional feedback they would like to provide:

Once they submit that rating, we'll track their responses for you.

All star ratings and feedback is available in all the booking export reports from the "Reports" page, and there is also a new report to only see appointments within a date range of your choice that have received a rating.