According to Apple’s website, the program, dubbed OS X Beta Seed, will allow users to sign up to gain beta access to Apple’s software. “Join the OS X Beta Seed Program and accept the Beta Seed and Confidentiality Agreement. Apple will provide a Beta Access Utility for your Mac, which gives you access to pre-release versions of OS X in the Mac App Store Updates panel.”
However this is Apple we’re talking about and naturally they’re pretty secretive about the stuff that they do, at least until they’re ready to show it to the world. For those interested in participating, you’d have to sign a confidentiality agreement which basically means that you’re not allowed to disclose the information that you have been given access to.
Of course there will come a stage where Apple will allow users to share information, as we have seen in the past regarding iOS and OS X betas, but presumably the early stages of the beta could be a closed one that Apple would rather not share with the world just yet. In any case if you’re interested in participating, head on over to the OS X Beta Seed program page for the details.