There are a few steps to complete to get private name servers working under WHM/cPanel.
1) Set your name server host-names under the "Basic WebHost Manager Setup" area in your WHM panel. You will see this link on the top left menu of your WHM.
2) Login to the cPanel for the domain of your name server host-names. Under the DNS section add an a-record for each host-name. You can use the following DNS cluster IP addresses for your name servers, 184.108.40.206 and 220.127.116.11.
3) Login to your domain registrar and add the name server host-names and IP addresses. Each registrar is different, but should provide you with a way to add your private name servers and their IP Addresses.
Once the 3 steps are completed you can direct your users to point their domains to use your DNS name servers at their domain registrar.