To submit system specs, Blizzard is requiring users to download and run a program. The point, according to them, is to get the most diverse array of system hardware and software possible, so that the game can be tested in numerous environments. The beta itself won't open for a few months yet, and will be available first to people in North America.
This is a somewhat unusual and new method of selecting beta testers, and though some might have reservations about submitting system specs it does seem like a novel way to get a lot of different profiles tested quickly. If you're willing to put up with those requirements, you can sign up here.