Newton's third law of motion states that "to every action there is an equal and opposite reaction". The statement means that if a body A exerts a force on body B, then B exerts an equal and opposite force on A along the same line of action.
Thus if a person strikes a wall with his fist, the force on the wall (action) is equal and opposite of the force on the fist (reaction) at the moment of impact.
When a bullet is fired from a gun, equal and opposite forces is exerted on the bullet and the gun. Owing to the action of the bullet goes in the forward direction and because of an equal and opposite reaction the gun experiences recoil in the backward direction.
Thus if a person strikes a wall with his fist, the force on the wall (action) is equal and opposite of the force on the fist (reaction) at the moment of impact.
When a bullet is fired from a gun, equal and opposite forces is exerted on the bullet and the gun. Owing to the action of the bullet goes in the forward direction and because of an equal and opposite reaction the gun experiences recoil in the backward direction.