The domain name which you registered with a registrar will not work until the DNS (Domain Name Systems) setup is completed. With the Name Servers you can setup A (Adress) records, CNAME and MX (Mail eXchange) records as you need for the domain.

A Records: The A record is associated with the IP address of the server which hosts the website. For example, if I registered the domain “aaa.com”, and the IP of the host on which my site is hosted is 11.11.11.11, I want to visit my site via domain www.aaa.com, then I need to setup a A Record.
You can setup multiple A records if needed.

CNAME Records:  A CNAME record is an alias to the real name. If I want to visit the site http://www.anotherdomain.com via the domain blog.aaa.com, I need to setup a CNAME record for it. The setup is similar to the A record setup but with CNAME records and domain (e.g. www.anotherdomain.com ) not IP address.
You could also setup multiple records to meet your need.

MX Records:  The A records and CNAME records are often used to setup a domain. But the MX record is required If an email server is setup to handle the mail accounts. The setup is similar but with MX records. There also can be multiple MX records (e.g. for backup mail servers).

NS (Name Server) Record:  The NS record is used to define the name servers for the domain. It is unnecessary to setup the NS records in the DNS entry because the NS records are already setup by the domain name registrar. In some case the NS records need to be changed to a new server for some purposes. Here is a example:

URL Forwarding:  Another way to point a domain to a website, even to a certain webpage is domain forwarding, which is also called URL Forwarding. It’s simpler than setting up records above.