With thousands of devices viewing your web site in thousands of different positions, the CSS Media Query attempts to display your site, the right way on each and every device. Wide thin, Portrait Land scrape, it all gets done with media queries.
My clients always ask, “What is a Responsive Web Design Media Query?” I Tell them it´s more or less a question of “IF.” If this is true, show that, If that is true, show em this, of none of this or that is true, take a break and go to the beach.
Media Queries are all about the situation of the If This or That built in a CSS file. See the video, What is a Responsive Web Design Media Query?