A Domain's Nameserver tells the domain where to point to. If you purchased a hosting Plan from HostXNow.com, you should have received an account information email which tells you what nameservers to point your domain to.
Just visit your domain registrar, click on the domain, and change the nameservers. Each registrar has a different method so please read their FAQs on how to change NameServers. We have listed some of the most popular domain registers on our DNS Changes articles. You may also want to create your own Private Nameservers or Custom Nameservers.
If you haven't received the email from HostXNow.com, it could be that your account has yet to be set up, or it has been delayed. You should also check your Spam/Junk mail folder.
If you do not receive a new hosting welcome email within an hour or so, please contact support for assistance.