General Settings > General
The subdomain you choose will usually be the name with which your customers will recognise you.
For example: If your business name is ABC Studios, there is a likelihood you will choose 'abcstudios' as your sub-domain. This will help your customers to easily find and recognise you in the internet.
The public schedule page and public buy page links that are formed are the direct links you can provide your customers for buying a pass or scheduling a class. The customer will still have to log in before buying or scheduling.
You can change your subdomain name if you really must but please note that you may have to change logos and other static text manually, where ever required.