*Well, almost every question, as the final StarCraft II: Wings of Liberty release date and the system specs required to play the StarCraft II multiplayer beta on PC are missing. But if you have other questions, Blizzard's FAQ has answers.
Burning questions like "How do I use my BlizzCon beta code?" are answered (Use it on the beta sign-up page.) as are details about what you'll be able to play during the multiplayer beta (Multiplayer ladder quick matches in 1v1, 2v2, and free-for-all (FFA) modes and unranked matches, but no single-player).
Just about everything you'll need to get up to speed on this month's beta is here.
StarCraft II Beta FAQ [Battle.net]