It's not just about media queries... one also needs to understand the concept of "fluid layouts" -- that is, declaring your widths in percentages instead of pixels. Media queries can help tweak a design to change/respond to different screen widths, but the first step is making sure your widths are fluid and flexible (otherwise you'd basically need separate media queries for every single pixel from 300 to 1000).
https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queri...
http://www.w3schools.com/css/css_rwd_mediaqueries.asp