Think of DNS (Domain Name System) as the phone book of the internet. Humans read words, computers read numbers. So when we type into our web browsers things like www.blueoceanwebhosting.com.au, we can read it but computers cannot. To enable web browsers to load the correct page we are looking for, web browsers like Google Chrome or Microsoft Edge interact through Internet Protocol (IP) addresses.
The DNS translates the domain names we read into IP addresses that the computer/browser can read.
Each device connected to the internet has its own unique IP address which other computers/devices use to find it. It is much easier to remember www.blueoceanwebhosting.com.au than 139.284.36.84 which the computer/browser can read.
The process of delivering a web page to your browser involves converting a hostname (example.com.au) into an IP address (262.258.36.365).
When you type in example.com.au, a request is sent to a DNS server to look up the domain you are trying to access. The DNS server (which there are multiple around the world) translates example.com.au into and IP address. The DNS server points your browser in the right direction as to where in the world that IP address is located – connection is made with the IP address, and the computer/device on the other end, starts serving the web page your after back to you.
This is DNS in its most simplest form – There are many more aspects to DNS eg the routing of mail.
DNS is very complicated business and incorrect DNS settings can be the reason for a lot of headaches.