You are playing tennis, and you strike the tennis ball with your racquet. 

1) An object at rest tends to remain at rest, and an object in motion tends to continue moving with a constant velocity, until acted upon by a net external force. 
* The tennis ball is moving in your direction, and it continues moving in your direction until you apply a force by striking it with the racquet. 

2) Acceleration equals force over mass (or "force equals mass times acceleration") 
* The harder you hit the ball, the more quickly it moves away from you, because you impart a greater acceleration to it. 

3) An action force of object A upon object B is accompanied with a reaction force equal in magnitude and opposite in direction, of object B upon object A. 
* The racquet exerts a forward force upon the ball, and thus the ball exerts an equal backward force upon the racquet, causing it to recoil from the impact.

Hope this helps:)
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