Here is the game : http://store.steampowered.com/app/730/

You will get a CD-Key that you'll have to activate it on the Steam platform.

Info :

Counter-Strike: Global Offensive (CS: GO) will expand upon the team-based action gameplay that it pioneered when it was launched 14 years ago. CS: GO features new maps, characters, and weapons and delivers updated versions of the classic CS content (de_dust, etc.). In addition, CS: GO will introduce new gameplay modes, matchmaking, leader boards, and more. "Counter-Strike took the gaming industry by surprise when the unlikely MOD became the most played online PC action game in the world almost immediately after its release in August 1999," said Doug Lombardi at Valve. "For the past 12 years, it has continued to be one of the most-played games in the world, headline competitive gaming tournaments and selling over 25 million units worldwide across the franchise. CS: GO promises to expand on CS' award-winning gameplay and deliver it to gamers on the PC as well as the next gen consoles and the Mac."

System Requirements :

WINDOWS

Minimum:

• OS: Windows® 7/Vista/XP
• Processor: Intel® Core™ 2 Duo E6600 or AMD Phenom™ X3 8750 processor or better
• Memory: 2 GB RAM
• Graphics: Video card must be 256 MB or more and should be a DirectX 9-compatible with support for Pixel Shader 3.0
• DirectX: Version 9.0c
• Storage: 15 GB available space

MAX OS X

Minimum:

• OS: MacOS X 10.6.6 or higher
• Processor: Intel Core Duo Processor (2GHz or better)
• Memory: 2 GB RAM
• Graphics: ATI Radeon HD 2400 or better / NVidia 8600M or better
• Storage: 15 GB available space

SteamOS + Linux Minimum:- OS: Ubuntu 12.04

• Processor: 64-bit Dual core from Intel or AMD at 2.8 GHz
• Memory: 4 GB RAM
• Graphics: nVidia GeForce 8600/9600GT, ATI/AMD Radeon HD2600/3600 (Graphic Drivers: nVidia 310, AMD 12.11), OpenGL 2.1
• Storage: 15 GB available space
• Sound Card: OpenAL Compatible Sound Card