You need a hosting account. That's where you get the nameserver information.
It works like this:
You register a domain at the registar. This is where your domain is "born" and lives until it's old enough to leave home. Sometimes domains never leave home and this is when registrars provide hosting. While not a crime, a domain that is old enough to leave home, should. People tend to look down on those that stay close to mommy and daddy. Also, if mom and dad take away the web site keys, you are stuck and at their mercy. Better to live free on your own.
-Next, you need a hosting account and should get one that is not where you domain is registered. Choosing a host is like choosing a wife except that if things don't work out there are no children, only subdomains to take care of, so getting a divorce is not too bad. Choosing a good host is a big topic so if you need help with that, and I think you do, just ask in a new topic.
Your hosting company will generally be the place that tells everyone the location of your domain and web site. It's like a house number. The list of addresses or domains the host is renting to is located on their nameserver(s). There are generally two and can be more.
To make your web site work, you need to get the nameserver addresses and go into your domain registrar account and edit your domain information to include the nameservers.
When someone enters your domain in a browser, the request is like a prayer sent off to heaven which is called the "Root servers" or in some cultures, "Verisign". The root servers are like god because they know the names off all livings souls (domains). They see and know everything and they know that your domain is at your registrar and then the request there. Then your registar looks in their system and sends the request to your hosting company's name servers who tell the browser where the web site is. Some of the details may not be exactly right, but this is about how it all works.
For a more clear and detailed answer, try Wikipedia.org.
You can also go to Google and enter "define:nameserver" for example, and get information.