DNS servers are Domain Name Servers. They translate names to IP addresses. On the Internet, technically everything works on IP addresses. Actually you don’t need to be concerned about how name servers work. However you are reading this because you are trying to understand the fundamental components that make Internet work.
It happens behind you.
This name to IP address (understand numbers) translation happens behind you. Nobody will ask you to learn it. However understand that without these servers, you would be left with cryptic, difficult to remember numbers to get to your favorite web destinations.
Without these servers you would have had to remember IP addresses like 18.104.22.168 instead of abcx.com which is highly impractical.
Before DNS servers – Some history.
During Internets olden days a file called hosts file with all names and corresponding IP addresses were maintained in servers which need to communicate to each other for converting names to IP addresses. So that name could be used while communicating instead of IP addresses.
Along with routers and web servers, Internet also contains large numbers of DNS servers so that names are easily converted to IP addresses. It is not a system by which a few servers do it all. It is a hierarchical system in which one server asks the next server and it asks the next server in the hierarchy and finally an answer is found at the server authorized to the name being looked for.
Next : How does it happen?