Subdomains are actually extensions of a website that are primarily used to separate and categorize web site content. The address of the subdomain appears before the main domain name. For example – subdomain.example.com. It does not cost money to add a subdomain to your web site, and many web hosting providers allow the use of unlimited subdomains.
By creating a subdomain you are actually creating a separate web site within your site, which can be used as its own independent directory. When content is uploaded to the subdomain via FTP, a new FTP account should be created for the subdomain to facilitate quicker access to the site's directories and files.