Responsive websites work by using media queries to detect the device or the resolution of the device being used to access them. Once this determination has been made, a combination of flexible images, type, and grids adjust to fit the screen on which the site is being viewed. If you want to see responsive design in action, adjust the size of your browser while viewing a site that has implemented responsive design. Mashable is a great example. The adjustments will enable you to see just what the designers had in mind when creating it and how different each stop can be.