The HTML5 test gives you one huge, bold number denoting your browser's HTML5 support level.
Simplicity is the key here: you just get a number. The number you see above is for Chrome Canary. Firefox 3.6.8 (my browsing workhorse) only scored 139 (and 4 bonus points).
It's important to understand that this is not a benchmark. It doesn't use any of the HTML5 features to render anything; the browser is simply asked, "do you support this?" and the site takes its word for it.
The "bonus points" come from audio/video codec support, as well as SVG and MathML for plain HTML. If that sounds like a bunch of acronyms I just stuck together, feel free to ignore it. What you should know is that the bonus is a bonus; not strictly HTML5, but stuff that usually goes along for the ride.
Another interesting aspect is that not every feature is worth one point. For example, the "Web applications" category has three tests, and is worth a total of 14 points. The "Gnolocation" group (under "Related specifications") has just one test, worth 10 points.
So the number you get isn't a count of features, but more of a weighted evaluation. Still, what's great about the site is its simplicity - it's a very easy way to convert people over to a more modern browser. Just have them point their trusty IE6 at HTML5Test, and then show them what you get on your awesome, modern browser. It's easy to understand, which is the whole point.