Videos
Is one better than the other or used differently, or is html5 just an updated version of HTML?
Not everyone is using them because not every legacy browser supports them. Most modern browsers do support HTML5 but there are still lots of folks on the internet that are using old, outdated browsers. Fortunately, some HTML5 tags have fallback options in which non-supported browsers load different tags depending on who is viewing them
Old tags are still around because they are still a crucial part of the HTML structure. Lots of websites rely on these "old" tags to still function and so taking them out would break a lot of websites. There is really nothing wrong with "old" tags and it all depends on your implementation and audience. Think of HTML5 as an addition to the HTML family and not a replacement
HTML5 offers cool new tags such as
<canvas>,<video>,<audio>, and more to bring the HTML language more in-line with modern times. Check out more about it at W3 here: http://www.w3schools.com/html/html5_intro.aspHTML5 is supported for most modern browsers. You can see a list of them here: http://html5test.com/results/desktop.html
I agree with Shaun. HTML5 is not a replacement for HTML, but an addition. To my understanding, HTML5 offers a more semantic approach towards coding the markup for a website. Also, HTML5 features more features such as sound, audio, canvas, video and greatly supports animation. If you wish to use the older HTML tags, you may do so.
But, if you wish to keep things more semantically accurate, use the HTML5 tags like <header>, <footer>, <aside> etc. HTML5 is still under development so it will be some time till all browsers support it. However, you might already be using plenty of HTML5 and CSS3 elements if you are using a framework like Bootstrap and it pretty much works on many browsers (except for infamous IE).