If object A and object B interact (collide), then object A will exert a force on object B and object B will exert an opposing force on object A, but in the opposite direction. 

For example, the force of the weight of an object on a table creates the simultaneous force of the table pushing up on the object; this is called the normal force.  When a collision occurs between two objects, they each simultaneously exert an equal and opposite force on each other.

One common misconception is that Newton's third law describes a cause-and-effect relationship (action leads to reaction). Another misconception is that the force pair acts on the same object. The force pair describes the forces that occur simultaneously as a result of an interaction between two objects.