The most important thing you should note is that there are no official beta keys. Blizzard opens the gates to their betas by granting access to your account — not sending you a beta key. If you’re in the beta, you’ll be able to download and play the WoW Classic client from your Battle.net launcher. If not, you aren’t in the beta. It’s easy to be tricked into thinking you’ll get a beta key from an email that looks like it’s from an official Blizzard address, but don’t believe their lies — they’re all fake.
The original World of Warcraft was released in 2004, and World of Warcraft Classic aims to recreate the state of the MMORPG before its first expansion, The Burning Crusade, was rolled out in January 2007. Previously, players looking for a “vanilla” version of the game were only able to experience it on custom servers such as Nostalrius, which Blizzard shut down in 2016 to protect its intellectual property.