In other words, if body A exerts a force on body B, B exerts an equal and opposite force on A. For example, if car A crashes into car B with a force of 10,000 N, then car B exerts a force of –10,000 N back on car A.
Newton’s Third Law
Further examples
When a girl jumps to shore off a boat, the boat moves backward. This is the reaction (boat moving backwards) to her action (jumping).
When a gun trigger is pulled, the gun exerts a force on the bullet or shell, pushing it forwards. The bullet exerts a force on the gun, pushing it backwards. This is the recoil.
When a rocket is launched, the engines exert a force on the gases pushing them backwards. The exhaust gas exerts a force on the rocket engines, pushing the rocket forwards.