What is the purpose of a free body diagram

The purpose of a free body diagram is to make  a visual representation of all the forces acting on an object.

In a free-body diagram, the object is represented at the centre; every force acting on the object is represented as an arrow, starting from the centre of the object, and with a length proportional to the magnitude of the force and direction equal to the direction of the corresponding force.

answer; how far out of place which the object finished relative to the starting location;