Space Farmers is a co-op game only and has no single player mode. Grab a friend, grab a gadget, grab a gun and get ready. Space Farmers is the most fun you'll ever have in a co-op game.In Space Farmers you and a friend will encounter gadgets, guns, puzzles, pigs, a horde of killer robots and more. This one of a kind co-operative action adventure will make you laugh, cry and bring the human race together.
Go to: http://store.steampowered.com/ and download STEAM client
Click "Install Steam" (from the upper right corner)
Install and start application, login with your Account name and Password (create one if you don't have).
Please follow these instructions to activate a new retail purchase on Steam:
Launch Steam and log into your Steam account.
Click the Games Menu.
Choose Activate a Product on Steam...
Follow the onscreen instructions to complete the process.
After successful code verification go to the "MY GAMES" tab and start downloading.