Responsive design means a website changes its layout to fit the screen it is being viewed on. It is like a piece of furniture that folds smaller for a compact room and opens up when there is more space.
A row of three cards might become a single column on a phone. Text, pictures, and controls should remain readable and usable at both sizes.
The goal is not to make every screen look identical. It is to make the same content work comfortably on different screens, including when someone zooms in.