Most multi-column layouts use multiple float:left divs inside a container div.
Lets have a look at a simple main column and sidebar column layout:
HTML:
<div class="main"> <div class="container clearfix"> <div class="content"> <section> <h1>This is the Main Content</h1> <hr> <h2>A sub heading</h2> <p>Lorem ipsum dolor sit amet, consectetur...</p> <p>Lorem ipsum dolor sit amet, consectetur...</p> <p>Lorem ipsum dolor sit amet, consectetur...</p> <p>Lorem ipsum dolor sit amet, consectetur...</p> <p>Lorem ipsum dolor sit amet, consectetur...</p> <p>Lorem ipsum dolor sit amet, consectetur...</p> </section> </div> <div class="sidebar"> <aside> <h2>This is a sidebar</h2> Sign up to the newsletter! </aside> </div> </div><!-- /.container --> </div><!-- /.main -->
Go here and paste the above code into the HTML pane.