The Appointment Booking Calendar has a visual form builder that appears on each calendar settings page to visually add/modify fields and set the validation rules.
If you want to use it instead the classic form then you can enable the form builder in the “troubleshoot area” located below the list of calendars.
The form builder is available & included in all the commercial versions of the plugin (Professional, Developer and Platinum versions).
The form builder and other features from the Professional version can be tested for free at the online demo of the plugin at these pages:
Administration area: http://www.dreamweaverdownloads.com/demos/appointment-booking-calendar/wp-login.php