A method rather than a tutorial -
step 1 - the player needs to have a sensor (ray/near to detect the vehicle) and the required key sensor, connected to an and controller, this should then make a player’s camera property “0”, call it “Active”, also have a camera actuator connected, this should change the camera to a camera parented to the car.
step 2 - parent the player to the car, using the ghost option on the actuator. make a short (easy) script that places the player at the position of an object (use a “no collision” emptymesh in the driver seat, for example). set the car’s camera’s “Active” property to be “1”.
step 3 - connect a property sensor when “Active” is equal to “1”. Then connect this to ALL the controllers connected with the controls of the player, and the same for the car object. this way, you can only drive the car when your player is in it, and you can only move the player when not in the car.
step 4 - toggle these properties again, and remove the parent of the player (perhaps using another script to place the player at the position of another “no collision” emptymesh, this should be perhaps at the door of the driver’s seat.
not sure of your level so I kept this at (what I hope is) an intermediate level… just describing some of the logic of the way it could work, good luck…