Log in to your Social Club account, or create a new one if you don’t already have one.
Select “Use Rockstar Code”, and then enter your unique code that's displayed on the 'Orders' page of CDKeys.com and follow the prompts to activate..
Select “Confirm” and then follow the prompts to download and install the game on your PC. You can find additional support with the Rockstar Social Club here: https://support.rockstargames.com/