SEVERAL EMAIL questions from people who are registering a domain name point to the fact that many people do not know that registering, parking and hosting services can be split up when it comes to web sites. I think there are times when you should register your domain name with one party and point your domain name through the Domain Name Server of another party. Having a third-party DNS provider gives you a level of abstraction that avoids having all your eggs in one basket. If you become dissatisfied with your domain registrar, you can switch to another registrar and not worry about what happens to the way your Domain Name is managed because your DNS entries will be with another service provider.
When you register a domain, in addition to your name as the registrant you should be asked for "Nameservers." Two are required, but most registrars will allow you to enter more. You can enter the names of any valid DNS servers in these fields.
When you signup with a DNS provider, they will assign you Nameservers which you enter into the specified fields in the domain registration. Once you do this, the specified Nameservers become "authoritative" for your domain so if anyone on the internet wants to know the iP address associated with YourDomain,com, it asked the Nameservers you specified.
Most people think web hosting stops at the WWW part of a web address. However, hosting a web site means being able to find the web address and that's a service performed by the DNS host. If you want to have the flexibility of controlling your DNS independent of your registrar, or if you want to have "dynamic DNS" you need to sign up with a DNS provider or run your own server.