Hi Don,
thanks for contacting us.
I.e. if you want to use hotels.london.co.za as a cname, first you need to point the cname hotels.london.co.za to https://www.booking.com: this can be done using your domain provider administration panel ( everyone is different ). This way hotels.london.co.za is associated to https://www.booking.com.
Then you need to communicate this cname to our support team.
Finally, once updated on our system too ( so your cname will be associated to your implementation and your aid ), you can fill the corresponding field in your search box plugin’s settings.
This way hotels.london.co.za will be shown instead of https://www.booking.com on browser’s address bar when a search is performed using search box widget of your website.
Does it make sense?
Let us know if there is something unclear and we’ll be happy to help!
Have a nice day.