Html5 is the latest version of Html and in html5 bring you responsive design and you can view on mobile even and there lot of function and features in html5
better guide you google
HTML5
2014 HTML5 – Proposed Recommendation and Recommendation
In September 2014, W3C moved HTML5 to Proposed Recommendation.
On 28 October 2014, HTML5 was released as a stable W3C Recommendation,meaning the specification process is complete.
HTML5 is the newest specification for HTML, and many browsers are going to start supporting it in the future. One nice thing about HTML5 is that it attempts to stay backwards compatible. So if you don't want to learn it just yet, you don't need to.