The Internet is a giant network of computers. To identify them, each computer is assigned an IP address, which is a series of numbers.
A series of numbers is quite difficult to remember. Domain names were invented to solve this problem. Now if you want to visit a website, you don’t need to enter a long string of numbers. Instead, you can visit it by typing an easy to remember domain name in your browser’s address bar.
Think of it like a mobile phone: you want to call your mother, so you simply click on your contact "Mom" and your phone dials your mother's phone number. Domains are connected to IP addresses in much the same way.