Got a Steam key and don’t really know what to do with it? Easy-peasy:
- Open the Steam application (or install it from here if you don’t have it)
- Click the “+ ADD A GAME” button (lower left)
- Choose “Activate a Product on Steam…”
- Mess about appropriately, and enter the key in the “Product Code” textbox
- Done – you’ll find the game under the LIBRARY tab