DNS is often called “the internet’s address book”. Its job is to turn the easy website name a person types into the string of numbers a computer actually needs to find that website — quietly, in a fraction of a second, every time.
Think of the contacts list in your phone: you tap the name “Mum”, and the phone looks up the real number and dials it. DNS does the same for websites — you type the name, and DNS looks up the matching numeric address so your browser knows where to go.
This is what connects a Domain (the name people type) to the Hosting where the site actually lives. When a new site is set up or moved, adjusting its DNS is what makes the name point to the right place.