If your domain is located in a subfolder of your hosting account, enter it's name here. Otherwise, if your domain ('mysite.com') points directly to the root folder of your hosting account, leave this blank.
If you aren't sure then chances are it's in the root, so leave this blank.
Note: Most servers label the root folder on your server as 'public_html', if your server differs then change the name here. The same holds true for the port number setting