If you integrate this system into your own web site then all you have to do is sprinkle links at your site that point to your online booking page.
On that page you will include all of the links that a client will need to book. A registration link, a link to their PAC, a link to recover login information, a link to your appointment book and so on.
If you don't have a web site then you will most likely select one of the home page options. That home page will have a unique sub-domain prefix within the system, such as
myname.beautybyus.com
It all depends on your own situation as to which option you select. If you don't currently have a domain then you can confidently rely on the quality and content of these home pages as a cost effective alternative.
to see for yourself.