If you're gonna learn about Canvas, you'll need to learn some JavaScript too, otherwise you won't be able to do much with your nice shiny <canvas> tag. It's just a rectangle on which you can draw stuff via JavaScript.
Contrary to what Peter says though, I do recommend getting a book (dunno which one, not read any of them), if only because it's handy having something there you can pick up and refer to whenever you need, even when you're not at the computer.
Oh and if you want something to help you learn JS,
Eloquent JavaScript is pretty good if you don't have much experience with programming in general. Even if you do, it's still quite useful. (I have the paperback version, but the full one is online too.)
edit:
Forgot to say, "HTML5" can mean more than one thing – lots of people seem to use it to mean "HTML 5 + CSS3 + Canvas". By itself, HTML5 is just a bunch of new tags, like <nav> and <section>, which isn't that exciting but does make your page more meaningful to search engines and stuff (rather than it being a forest of non-semantic <div>s).
EDITED: 21 Jun 2011 10:32 by CAER