I agree, more details are needed.
It really depaends on what your doing here. In Cpanel/WHM for example, you have to assign nameservers to IPs. Then your DNS record has to point to the nameservers. Then your domain has to have the namservers registered.
For example. i have mydomain.com. If it had ns1.myhost.com, i could create a host on my registrar called ns1.mydomain.com to point to the same IP. But if you are createing a new nameserver based on IPs you have, you would first need to create a DNS entry for them. For example, in WHM/Cpanel, There is a place to assign nameservers to IPs. Then you have to add a record to your DNS to pick it up.