When we opened the address of a website, for example www.google.com, then there is a mechanism (system) that will change the name of the address into the address understood by machines, which is the IP address (Internet Protocol / IP Addresses). The system is regulated by a protocol called Domain Name System / DNS.
With the DNS, then we do not need to remember IP addresses are hard to remember. For example www.google.com will translate into 74.125.200.139. So that we can directly open google by typing the IP address in the URL of the web browser we use. But this is certainly not efficient, because how many addresses like this that we have to memorize? so the DNS role is very important.