Why is my player still moving forward(north) in world coordinates? I want the player to face and move in a new direction. Please explain in simple terms.

void PlayerMover()
{
    _step = _speed * _speedMultiplier * Time.deltaTime;

    PlayerBoost();
    float vertical = Input.GetAxis("Vertical");

    PlayerRotation();

    Vector3 direction = new Vector3(-vertical, 0, 0);
    transform.TransformDirection(Vector3.forward);
    transform.position += direction * _step;
}

I am using C#/UNITY

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