Let us make it clearer HTML5 is the newest hypertext markup language for creating websites. Since 2011, people start writing markup codes on HTML5. At that time the support for different browsers are difficult for HTML 5 and many browsers support are very power as the language is started getting popular more and more browsers development companies started working into and made their browsers compatible for HTML5 markups. Nowadays all major browsers-chrome, IE, Mozilla, Safari supports HTML5. Few of the markup that really made it awesome are <video>, <audio> and <canvas>. However, all new markups are really of equal importance but these markups made the browsers less dependable in third party API and thus it is better than other versions. Apart of that, it made less dependent on scripting which are replaced by new markups. In addition, over all it is device independent which is the reals demand of the development process. Error handling is easier.
In near future we can find that many syntaxes will be dropped from the version and better syntaxes will be introduced or may be replaced by existing HTML5 syntaxes. Many syntaxes where created to run heavy content reach websites in small devices seamlessly. Integration of vector graphic content etc. are few of great features that introduced in HTML5.
One question arises where you can start writing HTML5 then my answer will be yes start it now. W3scools is the right place to start with but you may choose any other tutorial website, which you find best according to your understanding and convenience. Though having a good knowledge of HTML4.01 will really help you to master the new syntaxes as lot of syntaxes where taken from HTML4.01. Lot of frameworks were introduced which are based on HTML5 and you can refer them for developing rapid web applications.