It depends which DNS servers have been configured to be authoritative for your domain.
When you register a domain, generally the registrar's servers are configured by default to be the nameservers for your domain.
You can change this, to someone else's DNS service, or run your own.
If you've only got one server, and a small network, use someone else's servers. You don't want to worry about running a DNS infrastructure yourself. If there's only one site, and your host/registrar is reasonably well known, use theirs.
In order to bring up a new website, you need to know which servers are hosting the DNS Records for your domain name. The easiest way to figure this out is to run
whois yoursite.org and look for the nameserver lines in the response.
This is for example.org
Then you'll have some idea where to start looking for your DNS records to change for the new site.