Reserving for the first time! Excited and confused!

Hello. I'm completely in love with AaTP's new release, "The Empress Who Loved Death - Elisabeth". I want to reserve it but I'm unsure of how to go about it! I've never bought brand before so I really need help! 
I don't exactly understand the rules of agreement either. The translation through my internet must be wonky! Also, they say that they'll start accepting reservations on the 21 but I can already reserve it? I'm very confused!
Can anyone guide me through the process?