The Zodiac Online storyline centers around the twelve Chinese zodiac signs - the dragon, tiger, ox, etc. -- and their battle against a force of demons heralding doomsday. Your job is to help the zodiac envoy defeat the demons.
Beta keys are available through several outlets, including the Zodiac Online Facebook group, prearranged giveaways, and the "Good Wishes" program in which you register on the ZO site, leave good wishes in a forum thread, and receive your key. (Zodiac Online obviously isn't too shy about handing out beta keys.)
Closed beta is expected to last "several weeks depending on test results," and beta key information is available on the official site.