Responsive web design allows websites to be accessed from different devices by dynamically changing the layout depending on screen size, while maintaining overall navigation and interaction. Key aspects include using media queries to load different style sheets for different screen widths, starting with a mobile-first approach to load minimal resources, and techniques like srcset and picture to serve the most appropriate image assets. Designing breakpoints based on text length rather than fixed widths allows the layout to adapt better to varying screens. Unused JavaScript and resources can also be loaded conditionally based on media queries to improve performance.