If you ordered the Collector’s Edition of Homeworld Remastered, you’ll need to redeem your key included with your Collector’s Edition at http://www.homeworldremastered.com/redeem. Upon redeeming the code, you will receive your key to download the game through Steam.
To redeem the Steam key for your copy of Homeworld Remastered, first you’ll need a Steam account. Steam accounts are free and can be downloaded here - http://store.steampowered.com/
Once Steam has been downloaded and installed, run Steam and click “Games” at the toolbar across the top of the window, then click “Activate a Product on Steam”. You will be prompted to input your Steam key.
If you have trouble redeeming your code (code is smudged, misprinted, or you receive an error upon redemption) please submit a support ticket at support.gearboxsoftware.com