One of the most important things. BEWARE scams people! Nobody can give you a key. It has to be enabled on your Bnet account by Blizz.
Players selected to participate* will receive an email invitation directing them to download the game client directly from the Battle.net desktop app. As always, please be aware of phishing attempts—if you’re unsure whether your invitation is legitimate, please log in to your Battle.net account to verify that there is a Dragonflight Alpha license attached (under Your Game Accounts).
Servers are not up for it yet though.
Oh, and they put up a pinned post about it hours ago 