The left column is only shown to users on larger screens over 1200 pixels wide. Use it for elements of interest that are not key to the site but might help your users navigate around the site.
For instance if this is a blog you might show monthly archives, your latest tweets or flickr images. If this is an ecommerce site you could show products a user has recently clicked on or related items.
CSS3 gives us the ability to display different elements based on the size of screen available. Try resizing your browser horozontally to see how different elements are shown, hidden and resized based on the browser window size.
Screens come in all shapes and sizes, developers have become use to setting design widths to around 980px but with the explosion of smart phones and HD TVs the amount of information that can be shown on the screen can vary vastly. Fluid designs go some way to solving this problem but often cause other display problems.
The center column is for the main content of the website, if this is a blog your posts go here, if its an ecommerce site this is where your products go. The center column is always shown regardless of the screen size.
Take a look at the source code and copy the elements you need into your own project.
The following code in the header dictate which stylesheet is displayed based on width of the page.
<link rel="stylesheet" type="text/css" media="screen" href="style.css" />Certain older browsers don't support min-width or max-width so if they can't understand these we show the default two column layout.
The meta viewport tells browsers the the initial width to set the viewport, we set it to the width of the 1 column layout so that mobile devices how to display the page. In your code you might want to detect the browser and just show this to mobile devices.
<meta name="viewport" content="width=480" />
The right column is going to display to almost everyone apart from mobile traffic. Use it to display supporting features to your main content, navigation items, links to social media and advertising.
If the right column is essential to the functionality of your site try displaying it below your main column rather than hiding it all together for mobile traffic.