Computers think in numbers not words. There is a digital equivalent to the 'example-site-name.com.au' address. It will have the form of something like 203.123.132.6 ...
When you tell your Web browser to go to 'example-site-name.com.au' on the World Wide Web the computer consults an online database, which is part of what is called the Domain Name System, and matches the name to the number and then it goes to that address.
Copies of this online database are found on computers all around the world. These computers are called Domain Name Servers. The number for this computer which is closest to you in geographic location must included in your Internet installation. This is referred to as the DNS Number.