To see a responsive website in action, compare the layout of this site on a mobile device and desktop, or simply make your browser window smaller on a desktop. Notice how elements change size and position, yet are still easily accessible. That is the essence of a responsive website.
A standard website presents the same layout no matter which type of device is being used to view it. This can lead to a less than ideal user experience, especially on mobile devices. When a standard website is viewed on a smaller screen, users often have to zoom in to read text, links can be difficult to click on, and horizontal scrolling is necessary in order to see all of the content.
