Test area

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:

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?

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