Test area

Hello,
I'm quite new to web design, but I'm starting to create sites for myself and others.
I am looking for help / support / advice on how to best configure temporary storage sites in my existing domain.
So, while I'm building these sites, I can give the staging direction to the person I'm building so they can see the progress of the site and suggest changes.

that is to say:
site1.domain.com
site2.mydomain.com

I think the correct way to do it is through Cpanel using subdomains and all my sites will be wordpress sites, so I also have to create the databases and the users that use phpAdmin … I think … anyway I can help. The complete process and the best way to do this?
SEMrush

Also once you have finished making the site, what is the best way to replace the old site … so I would have to move the new site from my server to your server replacing the previous website.

I hope that all that makes sense and I would really appreciate the help.

Thanks in advance