Domain name system refers to Distributed hierarchical naming system.  In this it can be computers or any other network through Internet. The domain name makes it possible to give names to a group of Internet users. The domain name system also stores the other type of information like mails which accepts emails from a specified domain.  The IP (Internet Protocol) refers to the set of protocols used for internet and other networks. It is commonly referred as TCP/IP, Transmission Control Protocol and Internet Protocol which were the first two networking protocols.
The domain name registration refers to database of the domain names which are in top level domain. It is also called as NIC (Network Information Center) that is part of DNS of the Internet that stores the data of domain names. They are managed by IANA (Internet Assigned Numbers Authority) The IANA manages the top of the DNS tree by administrating the data
The domain name registration is the process of getting a domain name, before you have the domain. It must be checked that the domain is available and someone has not taken it before. The domain name is registered for a period of one year. You have to renew your domain by giving a payment for another year to make it active. The top level domains are .com, .net, .in etc.  The domain name with .in is the Internet domain name for Indian customers. The .in domain is used by individual and organization for Indian customers.
Some other types are: 
.co.in : This domain name is kept for banks, registered companies as well as trademark organizations.
.org.in: It is for non-profit units.
.net.in: It is kept for ISP providers.
.gen.in: It is for general use. 
Some zones are reserved for the use by qualified organizations in India.
.edu. in: It is kept for educational institutions.
.mil. in: It is for Indian army.
.gov .in: Indian government. 
To contact the domain registration there are there ways: Administrator, Technical and Billing. 

.in is the Internet country code top-level domain for India.
Domain name registration is the process of obtaining domain names and then making use of them for the designated period of time that was decided by the concerned parties at the time when their names were being registered.