Ok, let me try to understand this, and get you going..
You bought a domain name, like google.com and you want the sub-domain to point to your x10 site, not the whole domain, i.e. blah.google.com to point to your site? If so, there is 2 ways to do this:
GO to the site who hosts your domain and look for a place to modify records and add either one of these:
A Record
SUBDOMAIN A <IPAddress.of.x10.server.your.on>
When doing this, you'll need to go into either "parked domains" in cPanel and add it, or login to www.x10hosting.com/account and change the domain name there
Or, more easily you can do this:
CNAME Record
SUBDOMAIN CNAME myname.x10hosting.com
NO additional steps are required for this, as it just forwards your visitors to your x10 domain.