-- Use a ginormous ruler to measure the straight-line distance between the start-point and the end-point. It doesn't matter what route the car actually took to travel from start to finish. All that matters is the straight-line distance.
-- Write down the distance you measured with the straight ruler, and the direction the ruler is pointing.
-- That number and direction, together, are the displacement. It has a size and a direction. It's a vector.