Private nameservers are where your domain points to our nameservers so that your customers do not see our domain name on your account. If you do not set up private nameservers someone does a nameserver lookup on your domain it will show our nameservers.
Once you set up private nameservers when someone does a nameserver lookup on your domain it will show ns1.yourdomain.com and ns2.yourdomain.com which will mask that you are using our services. Your clients can also use ns1.yourdomain.com and ns2.yourdomain.com instead of the our nameservers.
Depending on what registar you used for your domain name you may be able to set up your private nameservers on your own or you may have to contact your registrar to have them set up for you.
For guides specific to your domain registrar take a look at the following guides below or refer to your domain registrar’s knowledgebase.