Domain Naming System (DNS), as name suggests it assigns various domain names with IP -Addresses. Every computer has DNS component named as 'hosts' located in 'C:\Windows\System32\drivers\etc'. Whenever you request the website from your browser, first it checks the host file whether the mapping is available with any IP or not. If the mapping is unavailable, then goes to local server (i.e., ISP) and root server(i.e.,cloud or internet). It returns your webpage as soon as it finds the requested domain Ip-address.
The thing is, there are usually three locations to fetch the user request.
1) Hosts
2) Local Server and
3) Root server or Cloud or Internet.
The process goes as hierarchy and it doesn't go further location whenever it finds the result.
Here you need to NUT-UP for hacking the DNS.