You have a user manual and tutorial that described JMS Multisites.
This is not in the scope of JMS Multisites to provide user manual for all the HTTP Server administration tool that should be provided by your hosting company.
We can not know all the possible hosting company administration tools and user interface to setup correctly your domain and subdomain.

So as soon as you want to setup a domain or a subdomain you have to refer to the documentation provided by your hosting provder and their admin tool.

The only case that we can document is the one that use subdirectories as this assume that you already have a domain or subdomain correctly configured.

We just have illustrated one case concerning cPanel that is a very popular administration tool.