When it is needed to use vector ?

Displacement, velocity and acceleration that are needed to describe the motion of an object along a straight line. We found that the directional aspect of these quantities can be taken care of by $(+)$ and $(-)$ signs, as in one dimension only two directions are possible.

But in order to describe motion of an object in two dimensions (a plane) or three dimensions (space), we need to use vectors to describe the above mentioned physical quantities.