How this works?
 

I got the key in mail, im a backer.
Do I still need to buy the game?

If not, how do I install it?

I've got Steam but I did not see download button,
maybe im missing something...

bottom left corner of the steam client there is a "add game" button.

Sweet, thank you very much. :D

Backers don't buy it.
 

You got a key for early access because you backed the kickstarter project. You don't have to buy the game.

At the top, left in steam click games, then activate a product. Paste or type your key there. That's it.
:Kaleun_Wink:

Yes, got it working.
Game is buggy so Im going to wait for a bit
so devs can fix more stuff..

Interesting game, thought.