Position vector is used to specify the position of a certain body. Knowing the position of a body is vital when it comes to describe the motion of that body. The position vector of an object is measured from the origin, in general. Suppose an object is placed in the space as shown-

On the other hand, the displacement of an object can also be defined as the vector distance between the initial point and the final point. Suppose an object travels from point A to point B in the path shown in the black curve-

The displacement of the particle would be the vector line AB, headed in the direction A to B. The direction of displacement vector is always headed from initial point to the final point.