I'm not too clear on the question but I'll answer it to what I think you're saying..
When an account is created in Plesk you can login using an FTP client that will take you to your root folder (httpdoc).
If you are a system admin and have ssh access you can access the root of any account in this directory on the server:
var/www/vhosts/(domainname)/httpdocs where the (domainname) is the domain of the account
Hope that helps or answers your questions, cheers!