What is DNS?
Your DNS or Domain Name Server is the system that allows your web site to be displayed when the user types in www.coolexample.com.
Name servers are the Internet's equivalent to a phone book. A name server maintains a directory of domain names that match certain IP addresses (computers). The information from all the name servers across the Internet is gathered in a central registry.
This makes it possible for people across the Internet to access your Web site using a familiar domain name, instead of having to remember a series of numbers
It usually takes about 4-8 hours for .com and .net domains and about 24-48 hours for all other domain extensions before name servers on other networks are able to access the information after the central registry gets it. This period is referred to as the propagation period.