No, they're more like new options that give you more control over the central page element, and so, make it easy to create web pages, nothing more.
You can absolutely use HTML5 without using all those new tags. Just create a simple .html file, then add whatever you want. The choice of the tags depends on what you want to do. You can read this : http://www.w3.org/html/wg/drafts/html/master/syntax.html#the-doctype