In the Client Area tab, within the Settings menu, once you enable your Client Area you can choose a custom client area name which becomes part of the website link/URL that your clients can visit to make bookings, buy services and login to the general client area.
For example, if the name you choose is "businessname", then the link (i.e website address) your clients can access will be "https://businessname.ptminder.com". It's common for trainers to then link to this address from their own existing website or social media accounts, so clients can easily make bookings etc.
Here is an example of these settings:
If you get new clients who signing up with a new account through the Mobile Apps, in order to link to your PTminder account they will be prompted to enter your 'Client Area Name', in the example above that would be "businessname". Of course, if your clients already have their own login, then they don't need to worry about this as it's already linked to your PTminder account.
You can change the Client Area Name at any time, as long as it hasn't already been taken by someone else. If you do change it, then you would also need to update any links you have pointing to it, and possibly inform your clients.
If you do have your own website elsewhere, you can check the "I already have my own website" box and enter your website address. Doing so will mean your own website address will be used on the links in various emails which your clients may receive, so they will be directed to your website instead.