According to Google, the author tag markup enables websites to "publicly link within their site from content to author pages." This means that if you were to use the markup, you would be able to connect all of the articles to an individual author page (which is what Google will likely include on search results pages). The author pages, according to the announcement, will describe and identify the author, and can include content like the author's bio and photo, articles and other links.
Authorship markup uses the "rel" attribute in links to indicate the relationship between a content page and an author page. For example:
If you are already doing structured data markup using microdata from schema.org, Google will interpret that authorship information as well.
An important "usage" cue was provided by Google in that the rel=author link must point to an author page on the same site as the content page. The benefit of using authorship markup and remaining consistent in usage is that search engines and other web services will be able to identify works by the same author more easily.
Google has worked with several sites to markup their pages, including The New York Times, The Washington Post, CNET, Entertainment Weekly, The New Yorker and others. Google has also added the markup to everything hosted by YouTube and Blogger. In the future, both platforms will automatically include this markup when content is published.