Hi,
To use an external domain (i.e. not one registered via x10) you must do two things:
1. Point your domain to use x10's name servers, which are ns1.x10hosting.com and ns2.x10hosting.com
2. Add your domain via "Add-On Domains" in your cPanel.
Once this is done, your domain should then point to your hosting.
Thanks for choosing x10,
Ciaran C (Termz)