Structural elements in HTML5

<header>

Specifies a header for a document or a section. Can have several header elements for a page. You cannot place header tag within a footer, address or another header

<footer>

Just like header defines a footer for a document or a section. It typically contains author of the document, copyright information etc. You can have several footers

<article>

Specifies a independent, self-contained content. It should make sense of its own. You can typically use article element for Forum posts, blog posts, comments etc.

<aside>

Defines some content aside from the content it is placed in. It should be related to the surrounding content.  Appears in a side

<nav>

Defines a set of navigational links. Not all links of a document should be inside a <nav> element. It is intended only for major block of navigational links (such as menu). Screen readers for disabled can use this element  to determine whether to omit the rendering of this content.

<section>

Defines sections in a document, such as chapters, headers, footers. It's like a div. 

Above I listed basic info about some of the html5 elements. You might be asking yourselves why use html5 elements instead of <div>? These are included in html5 as for the move towards semantic web. Semantic web helps programmers understand the DOM structure better and also allows search engines to have a clear picture about the web page. It also helps screen readers to better parse the content as per there needs.

Stackoverflow : HTML5 Best Practices 

More elements on W3Schools