If you have created a website and wish to upload it to your webspace, you must upload it into the HTTPDOCS folder. You can create subfolders also within the HTTPDOCS folder but your main index page must be within the HTTPDOCS folder.
To upload your files you will need an FTP client. There are lots of free FTP clients available on the web. We provide video tutorials at the below link for a number of popular FTP clients under "FTP (Uploading your website)"
http://www.myhost.ie/support/tutorials/
When connecting to your site with your FTP software you will be prompted for a User name and Password. You can set these from the Plesk Control Panel, click on your domain, then under Hosting click the Setup icon, under Preferences you will see the FTP User Name and can specify your password.