Responsive design is all about having your web content respond, appear and work appropriately on whatever screen it’s on. Without creating multiple sites. Now I could point you to mediaqueri.es to show you real world examples, but being the visual person I am I thought I’d build my own that more effectively illustrates the concept:
Responsive Design, Illustrated (resize the browser)
I’ve also created three other examples. Because, lets face it, designing for mobile is like packing a suitcase. See what’s in ours: