There are hundreds of HTML5 resources on the Internet. One of my favorite is Dive Into HTML5. If you want an excellent introduction to HTML5, this is a good place to start. It’s written by Mark Pilgrim where he dissects all facets of HTML5 into ten chapters.
He starts out with a brief history of HTML, followed by how to detect HTML5, the details of the head elements, the markup, canvas, video, geolocation, local storage, offline applications and forms. The website also includes an Appendix of HTML5 elements.
This is an excellent read for those wanting to jump in and learn HTML5 quickly. If you want a hard copy, I recommend two books. One book is by Mark Pilgrim’s called, “HTML5: Up and Running.” The other is a book by Bruce Lawson and Remy Sharp’s called, “Introducing HTML5.”