For all appointments, services & products the default fields that appear are Full Name, and Email Address. There is the ability to add specific phone number fields, checkboxes which are great for agreeing to terms and conditions or GDPR and more.
If you would like to request additional information from your users/customers on your booking form modal, please watch this tutorial video on how to add these custom fields:
Custom Fields is accessed by clicking on the following icon in your admin area:
I hope that answers your question and if you have any others, please use the chat button on the bottom right of your screen to ask me another!