Human: Fall Flat for PC available only at Steam Digital Store. At other digital stores you can buy only Steam Keys for activation at Steam Store. Human: Fall Flat is a non-free game, so you can get it for free at all, maybe with a discount. 

Download Human: Fall Flat from Steam

1. You need to register the Steam account (need email and phone number for verification).

2. Install Steam at you PC.

3. Sign in to your account and go to the Store page.

4. Use the Search box to find Human: Fall Flat

5. Check the system requirements for your PC.

6. Add to card and purchase the game (use credit card, gift card).

7. Download and install the game from Library page to your PC. 

You will find a more detailed guide on the wikihow.

Important: Do not install games with torrents or other unofficial resources, as these files can damage your computer.