To Enter & activate Cheat codes in GTA 5 PC, Just Press this button ( ~ ) on your keyboard to bring a Small box, Type the Cheat in the box then hit Enter button on your keyboard.
Related Page – List of All Cheats of GTA 5 PC with pdf download link
Let us understand with an example –
If I have to Activate cheat for getting a helicopter. then First I will Open the Story mode of the GTA 5 game, then I will Press ~ this button on my computer keyboard, then I will Type the helicopter cheat code – BUZZOFF . Then I will hit Enter button on my keyboard.
Note: you can hit Esc button on your keyboard for Removing the Box which comes after pressing ~ this button.