HTML 5 is a new standard which has been introduced in 2012. It would replace HTML 4.01 which was introduced in 1999. All major browsers support HTML 5 up to some extent and their support is getting enhanced in new versions of these browsers.
Here is a basic structure of HTM5 document:
To handle IE lower versions using CSS, we need to write:

HTML 5 New Features
There are many new things have been introduced:
1. New elements like header, nav, section, article, footer.
2. Support for 2D drawing using "canvas" element.
3. For media playback, there are video and audio elements available.
4. Many more features which would be discussed in later lessons.