Mobile-First Design is an approach that designs the smallest screen experience first, then enhances the layout for tablets and desktops.
It matters because a website is often the first serious evaluation point for a buyer. Good design reduces confusion, builds trust quickly, supports accessibility, and helps visitors take the next step without feeling pushed.
Example
A designer first arranges a restaurant’s menu, hours and booking link for a narrow phone screen. On larger screens, the layout can add columns and larger photography without making essential information depend on desktop space.