The feedback request feature is automatically generated when you create an event. During the creation or editing of an event, in Step 5 - Filters & Settings you are given the option to have an automatic email sent out to all attendees who registered for that event shortly after the event has finished on that day. Be sure to have this function checked if you want each attendee to receive the feedback request email.
If you do not want an email sent to the entire group of registered participants, disable the automatic feedback request option.
Whether an automatic email goes out or not, you also have the option to pick and choose which attendee you would like to request feedback from.
To get selective feedback, select the desired class and desired attendee(s), or go directly to the attendee registration card. Once you select the attendee, their registration card will open. Select the Feedback tab and you will see the option to initiate a feedback request. You can do this for as many attendees as you like, and anytime you feel it is appropriate.