Step by step.
WHERE
cPanel, Domains, Create A Domain, or the Subdomains tool depending on your cPanel version.
WHAT TO ENTER
The subdomain prefix The domain it belongs to The document root, which cPanel suggests
THE DOCUMENT ROOT
Where the files live. Accept the suggestion unless you have a reason not to.
Note it. You will need it when uploading files.
AFTER CREATING IT
If your nameservers are ours, it resolves automatically.
If DNS is elsewhere, you must add an A record there.
THAT SECOND CASE
cPanel creating the subdomain does not make it resolve if your DNS is external.
The record must exist where your DNS actually lives.
That catches people out repeatedly.
RUN AUTOSSL
After it resolves, so the subdomain has a certificate.
Without one, visitors see a browser warning.
TESTING
Load the subdomain. You should see an empty directory or your uploaded content.
