First of all, just in case you are asking What are nameservers? Now that is out of the way.
When creating private nameservers, you must register at least two.
To register private nameservers with Namecheap.com, log in to your customer account and then follow this guide.
1. Locate the domain you wish to create the name servers for and click ‘Name Server Registration’.
2. Select the name of your first name server in the first ‘Host.Domainname’ dropdown
Note: These are usually ns1 or dns1
2. Enter the IP address associated with your name server in the first ‘IP Address’ field.
3. To create your second name server, select ns2 in the second ‘Host.Domainname’ dropdown.
4. Enter the IP address associated with your name server in the second ‘IP Address’ field.
5. Click ‘Add Name Servers’ to create the new name servers.
Note: When creating private nameservers, it may take up to 72 hours for these to propagate throughout the internet.