Newton's 3rd Law states that to every action, there's an equal and opposite reaction, which means action and reaction are equal and opposite. The law imples that when a body A exerts a force F on a body B, the body B will always exert a force F′ on the body A. The forces F and F′ are equal in magnitude but opposite in direction and since force is a vector, we write F = −F′. F is the action force, F′ is the reaction force. For example, when you push down on your desk with your fingers, the desk pushes up on your fingers with an equal force. If you hit a wall with your head, the force exerted by your head acts on the wall; at the same time the wall exerts an equal and opposite force on your head. You'll feel this reaction as pain in your head.
In the above examples, either force may be considered the action and the other treated as the reaction. In the everyday life of Science and Technology, Newton's 3rd Law is applicable to:
a. the recoil of a gun
b. jet and rocket propulsion
c. humans walking everyday etc.