Domain name is a name that is used to represent a group of numbers called IP address.
An IP address(internet protocol) is a unique set of numbers assigned to each computer on the internet.
Domain names were created to make IP addresses more human friendly.
Just think of an IP address as a street address. They identify where computers are located on the internet.
In order not to make the internet protocols sound complicated or abstract when humans communicate with computers on the network using internet, domain names were formed to help out in that regards.