how to turn an object left or right?

hello I am new to unity and I have a problem I hope someone helps me
I have a car in the scene which automatically goes forward.I want code that does this: when I press left arrows it turns 90 degrees to left position and continue its path to the direction it has turned.
I have used position.left code but it just moves the entire car to the left and it doesn’t turn to the new direction.
please help!

That turns the car 90 degrees to the left:

transform.Rotate(Vector3.up, -90);