Hi, its well described here. Im using HTML 5 myself and I really recommend you to do it best regards, stasiek
HTML5 comes with many new elements like section, article, footer, nav, header and side etc. and also with new attributes for the old elements. It has more great features like improved web forms handling, APIs for web application development to increase the performance of the website in the comparison of the HTML4.
HTML5 has a 5 on the end of it. And that makes all the difference. From now on, all elements must end with a 5. Like <div5> and <p5>