You will remember that the role of HTML is to store semantic content, while the role of CSS is to abstract presentational information from this content. But, as you have probably observed, the <div> tag does not tell us much about the content that it encapsulates and only provides semantic information about this content through the use of ids or classes. Since this is somewhat against the spirit of abstracting presentational information from semantic content, the new HTML5 standard introduces some extra tags allow more semantically specific markup, often replacing the heavy reliance on the <div> tag in the older HTML4 standard. This optional chapter addresses these new tags. Most readers can skim up to the heading "New Semantic Elements in HTML5," but before using these new tags, it would be worth your time to read up on compatibility issues in HTML5 - which are addressed throughout Mark Pilgrim's book.
Drawing on the multi-column layout you created using <div> tags and the HTML4 standard, try to "port" this website to the HTML5 standard using the information in Pilgrim's chapter.