dns stands for domain name Server, which is a computer responsible for translating domain names into IP addresses. It also provides details of the mail server responsible for handling your domains email. dns values are normally set to your ISP - if you're unsure what to do (or what any of this means), ask them - and they'll tell you what values to set.
If you don't have an ISP, or don't want to use their name servers, you can use ours for the purpose of URL forwarding. New registrations will be set to our name servers by default, but can be reset to other servers manually at any time. Please note that setting dns values to a particular server, including ours, is only half of the story.
The name servers themselves must be configured to recognise your domain name. In the case of using our name servers, you can update this information yourself through the management interface - using the URL forwarding feature. If you're using an ISP's nameservers, you will have to ask them.