We talked about the canvas element’s 2D context in this book, but there’s another specification in progress that describes how to work with 3D objects. The WebGL11 specification isn’t part of HTML5, but Apple, Google, Opera, and Mozilla are part of the working group and have implemented some support in their browsers.
Working with 3D graphics is well beyond the scope of this book, but the site Learning WebGL12 has some great examples and tutorials.