By default all files which can be accessed over the web are located under the /www directory. On the /www level you will find the directories which store the files for your subdomains (e.g sub.example.com), including the directory where your main web site files should be uploaded (e.g www.example.com). So, the files for your main web site must be uploaded in the /www/www directory. This is your web root folder.
In case you need to upload files to a subdomain you have created, its files should be uploaded to the corresponding subdomain folder. For example, if you have a subdomain http://gallery.example.com (gallery is the subdomain name) its webroot folder on your account will be /www/gallery/.
In case you wish to upload files to a location which is outside your webroot, you can use the Private directory.