You can easily create sub-domains of your main domain name from your control panel. Sub-domains are in the format http://subdomain.yourdomain.com. This is useful if you wish to segregate and identify different sections of your website by host address, e.g. http://sales.mydomain.com, http://enquiries.mydomain.com, http://support.mydomain.com etc.
Sub-domains are created with their own content directory on the file system, and can be assigned unique FTP login details appart from the main account FTP login.