The sub domain name is the third or lower level domain name that points to a sub folder for the domain. For example the sub domain ‘http://mysub.domain.com’ will point to ‘http://domain.com/mysub’. The sub domain will treat the sub folder as its root directory. Creating a subdomain through the Helm Control Panel is easily accomplished.
Log into your HELM control panel.
Click on the Domains icon.
Click on the Domain which you like to create the sub domain for.
Click the icon which says Sub Domains.
As you can see, this domain currently has no sub domains. Click Add New.
Type a header name for the sub domain. Click Save.
You will now see the sub domain has been created. Helm will automatically create a folder under the main domain in IIS with the same of the sub domain. This is where the files for this site will need to be installed under.