Key activation instructions:
1. Download (http://steampowered.com/download/SteamInstall.msi) or launch the Steam client.
2. Log in or register a new account on steam.
3. In the lower left corner, click on "+ Add game", and then click on "Activate on Steam" and enter the activation key for the game, which you will receive after payment.
After that, the game will appear in the "Library" section.

Windows:
Minimum:
OS: Windows XP
Processor: Intel Core Duo or equivalent
Memory: 4 GB RAM
Graphics: onboard graphics
Storage: 800 MB available space

Recommended:
OS: Windows 7
Processor: Intel i3 or equivalent
Memory: 6 GB RAM
Graphics: discrete video card
Storage: 800 MB available space

MacOS X:
Minimum:
OS: OS X
Processor: Intel Core Duo or equivalent
Memory: 4 GB RAM
Graphics: onboard graphics
Storage: 800 MB available space

Recommended:
OS: OS X
Processor: Intel i3 or equivalent
Memory: 6 GB RAM
Graphics: discrete video card
Storage: 800 MB available space

SteamOS + Linux:
Minimum:
OS: Any
Processor: Intel Core Duo or equivalent
Memory: 4 GB RAM
Graphics: onboard graphics
Storage: 800 MB available space

Recommended:
OS: Any
Processor: Intel i3 or equivalent
Memory: 6 GB RAM
Graphics: discrete video card
Storage: 800 MB available space