In order to redeem your key, follow the instructions below:
1. Go to official Rockstar activation page and log into your Rockstar Games Social Club account. Click "Join Social Club" if you don't have an account.
2. Enter your code on the Social Club Activation page and download the setup tool.
3. Download your game.
In case of any issue with game download please follow the instruction below:
Once connected, you should click on the cog at the top right corner of the screen. On "download games" in the menu, you will be able to select "Download for Windows".