All your files are currently in the public web root folder.
The 'inside' of your root is your publichtml/
. Everything you place in there will be publicly accessible.
The name of your root can vary from host to host, often public_html
or httpdocs
.
The 'outside' is one directory up. But remember some hosts do not give enough permissions.
You cannot test documents outside your root, because they are not accessible. Only something like PHP can access those files. That's why you do not place your img/JS/CSS files outside the root cause they need direct access. You can however serve them through your PHP.