The PDF rulebook is free if you pre-order the starter set, which contains everything you need to play. It?s been released early so you can read the rules before the starter set arrives so you can get up to speed quicker.
I?m not sure why you thought that a game that has not yet been released was going to be playable yet, especially as it says this on the website:
Please note: the rulebook on its own is not sufficient to play the game. You will also need gaming cards, dice, tokens, model warriors and terrain.
Did you not read that bit?