What is DNS? What is it used for?

DNS (Domain Name Systems) is a protocol used for converting domain names into IP addresses.

computer networking (at layer 3 of the OSP model) is done with IP addresses but for as humans it's hard to remember IP addresses, it's much easier to remember names. This why we need something such as DNS to convert any domain name we type into an IP address. You can think on DNS as a huge phonebook or database where each corresponding name has an IP.