You would upload the files into the httpdocs directory for your main files and any cgi or perl scripts into the cgi-bin folder.
For the site, you should be able to use the site preview icon in plesk to see your site. Is the server Windows or Linux, though?
In Linux, the url format for site preview would be the following:https://IP:8443/sitepreview/http/domain.com/
(that's what it is on mine anyway)
In Windows, the url format for site preview would be the following:http://IP/$sitepreview/domain.com/
If you want to see folders within the domain, you'd append the folder's name at the end.
Have a Blessed Day