On the Web, the domain name is that part of the Uniform Resource Locator(URL) that tells a domain name server using the domain name system (DNS) whether and where to forward a request for a Web page. The domain name is mapped to an IP address (which represents a physical point on the Internet).
More than one domain name can be mapped to the same Internet address. This allows multiple individuals, businesses, and organizations to have separate Internet identities while sharing the same Internet server.
A domain name server (also called DNS) is the Internet's equivalent to a phone book. A domain name server maintains a directory of domain names and their matching IP addresses. This information allows other computers to know where to go to find your website.
How? The information from all the domain name servers across the Internet is gathered into a Central Registry. Computer networks across the world check in with the Central Registry on a regular basis to get updates so they will know information about your domain and where to find your domain name or your website if you have one.
Without a domain name server and the information it provides, computers wouldn't know where to find your website or any other website.
It takes approximately 48 hours for your new or modified information that is entered into a domain name server to make it's way across the internet.