First you would need to assign IPs to NS1 and NS2 DNS on your VPS or dedicated server, or (if you are using shared hosting) get the DNS IPs from your hosting provider.
Then you would need to take that information to your domain registrar, and enter it in your domain name settings with them.
Allow 24-48 hours for the changes to fully propagate and traffic should resolve to your website.
You can do a WHOIS check after you make the changes to see if they have propagated.