How does a free-body diagram tell you about the net force on an object?

A free-body diagram shows the vectors for all the force acting on the body the resultant vector found by summing all the individual vectors represents the net force.

Using Diagrams to Depict ForcesWhen learning about force diagrams, you saw that scientists draw a diagram using arrows to show the type and size of the force. The object is shown as a small box or dot from which the arrows originate. These diagrams are also called free-body diagrams. A "free body" is one object drawn all by itself, even though that object is likely to be in contact with other objects. This way you can focus all your attention on what is happening to that one object.