When one have zPanel, one may realise there is no web based File Manager in zPanel.

So the way to upload website files is this:
a) setup some FTP account (i was unsuccessfull, if you succeeded, pleas ekindly share on how to do it)
b) use software like WinSCP to transfer files via SSH to your server

The www path for zPanel is:

If one want to have file accessible via IP (http://YourServerIP/yourfile.php), then upload yourfile.php into: /etc/zpanel/panel

Files permission should be 0644 and folder permission 0755.