When you are setting up Ubuntu the DNS servers that are being asked for are the upstream nameservers. These should be the IP addresses of the nameservers provided by your ISP. You may want to use Google's nameservers, or those provided by OpenDNS.
If you have a home router, you can usually use its IP address as a nameserver. Hosts that use DHCP to get their IP address usually get their DNS nameservers that way.
All domains have their own nameservers which host the names for that domain. Unless you understand DNS quite well, it is best to use the nameservers provided by your registrar for this purpose.
In your case with Hover, you want to use Hover's DNS servers. Add an A record for your domain with the external IP address of your router. Your router will then handle routing connections to the server using your port forwarding.