How to configure patient appointment booking via website user portal

I am using v15-beta. I am trying to figure out how to enable booking appointments by patients in website user portal.
I do this by going to my account and filling patient appointment form. Problem is i can only create appointments for patients already registered in back-end desk view. New user signup are not automatically added as patients. what should i do to so that all new signups in website user portal are added to patient master automatically.
secondly the patient appointment booking section in website user portal is just using form where i have to enter values manually and it doesnot even show availabilty. What can i do so that the patient appointment form is replaced with the new patient appointment flow that is shown in desk view.