Activating a Rockstar key is really easy, simply follow these short steps:
Redeem your product code in the Rockstar app
Log in to your Rockstar account via Rockstar Game Launcher,
Navigate to the Store Tab,
Select Redeem Code button,
Enter your code and proceed with activation.
Redeem your product code with the website
Go to socialclub.rockstargames.com and log in to your account
Click on your avatar in the top right corner and choose Game Activation.
Find the game you want to activate and click Use Rockstar Code.
In the next window type your code and click Activate.
Click the Confirm button
Now just click Download for Windows and that's it - enjoy the game!
Once you’ve redeemed your code, your game will appear in your account.