DNS (Domain Name System) is a service that translates domain names into IP addresses. When you visit a website, you're not actually visiting the domain name, rather you're visiting the IP address the domain is pointing at.
Without DNS, we'd have to type IP addresses rather than domain names. It's all thanks to DNS that we don't have to remember every single website's IP address we visit, rather we simply type in the URL in characters to visit our destination.
