HTML is the basic language that web pages are built on. It stands for 'Hyper Text Markup Language". It is the basic language used to build web pages. If you right click on this page and choose "View Source" ... or whatever similar option your browser uses, you will see the HTML that makes up this very web page.
You web browser reads the HTML and then interprets it to paint this page. There are minor differences in the way different browsers can interpret the same HTML. That is why the same page will sometimes look different in IE than it Chrome or Mozilla.
HTML 5 is simply slated to be the next version of the HTML standard. As far as I know, it is not fully set yet. Understand, this will simply be a standard set by a committee known as the W3C, or World Wide Web Consortium. It will merely be a set of suggested rules. There will be no legal obligation for any web browser to actually implement this standard, and it is not uncommon for various browsers to deviate somewhat from the standard set by W3C.
So, I guess you could say that HTML 5 won't really DO anything. In fact, it will have no effect at all until browsers and web developers start following. It will just be a suggested standard, and it will be anyone's guess how soon or how closely the various makers of web-browsers will implement it.
Plus, I've been developing software since before most people knew that there WAS an Internet.