How to play Kingmakers right now
You can’t buy it, pre-order it or download a demo yet. The one route to actually playing is an invitation to the Steam playtest. Everything else you can do today is about being first in line when that changes.
Four things you can do today
Step 1
Request the Steam playtest
The only way to play before release. Press Request Access on the store page and Steam emails you if you are invited.
Step 2
Wishlist or follow it
On the same page. The official FAQ points players to the Steam wishlist for updates on the game.
Step 3
Watch the Gameplay Deep Dive
Twelve minutes of the developers playing and explaining it. It is the video below.
Step 4
Join the official Discord
Linked from the studio's own Steam announcements. The developers have pointed players there for playtest news before.
The playtest steps, and what nobody has said about places or NDAs, are on the Kingmakers playtest page.
What you cannot do yet
Be careful with downloads
Because the game is not on sale anywhere, a site offering a Kingmakers download, a free copy or a key is not giving you the game. The two real store pages are Steam and the Epic Games Store, and the official site links to both.
Getting ready for when you do get in
The practical checks are the same whether you are invited to the playtest or wait for Early Access: whether your PC is close to the listed hardware (Kingmakers system requirements), whether you plan to play with friends (Kingmakers co-op), and whether you expect to use a controller, which the Steam page does not currently list (Kingmakers controller support).
This site is the Kingmakers wiki for that waiting period: everything above is tied to what the developers have published, and the full list is on sources.