FORCE
Forces are all around us, and you could probably name a few, like friction and gravity. Forces have a definite strength (magnitude) and direction which make them vectors, like velocity or acceleration. Forces seem to cause motion but how do they really work? You are in good company when you ask this question. This is a question that plagued the early physicists like Aristotle and Galileo. They guessed that it took a force to keep an object moving, and if all the forces were removed an object would just stop and stay where it was. Does this make sense? Earlier when you were researching different kinds of motion you found rest is just another form of a constant velocity. So is not moving special in some way? That seems a little fishy to me; how does it seem to you? Think about driving in a car. The car next to you doesn't appear to be moving because its moving the same speed as you. The car you notice is the one thats speeding up and slowing and weaving in and out of traffic.

INERTIA
If you thought that sounds a little fishy you are not alone. Sir Isaac Newton (not of the fig family) thought so too, and in 1686 he caused quite a stir when he was able to explain almost all motion (and I mean all motion), from the planets to you falling down the steps, with three laws called quite appropriately Newton's Three Laws of Motion. The First Law said that if you removed all forces an object it would keep on moving or not moving as the case may be in a straight line just as it had been before the forces were removed. This law is usually stated: An object in motion will stay in motion and an object at rest will stay at rest unless it is acted on by an outside force.  When we push an object it moves for a bit then stops this is because the force of friction is acting on it. If friction were not there like on a shuffleboard table the object would just keep going. If you  have ever played shuffle board when you hit the puck it doesn't slow down or change direction until something forces it to (your opponent hitting it or a wall). This property of matter is called inertia and that is why Newton's First Law is often called the Law of Inertia.

NEWTON'S SECOND LAW
What we see is not the force itself but the change in motion or acceleration that is caused by the force. The amount of acceleration a force causes is related to how massive an object is. Think about when you are trying to push something: the lighter an object, the easier it is to push; the heavier an object, the harder it is to push. This relation yields the only equation you need to know:

ACTION AND REACTION
Newton's Third Law of Motion (probably the one you are most familiar with). It is often stated as: For every action there is an equal and opposite reaction. So if you push something exerting a force on it, according to this law it exerts a force on you right back. Then why does anything move? Why aren't we all stuck in place?  The answer is given by Newton's second law. The forces exerted are equal but the amount of acceleration we see is determined by the mass of the object. Think for a second about this example. You are pushing on the earth with some force maybe you are doing a pushup. The earth is pushing back at you according to Newton's third law and you accelerate upwards, but the earth does not appear to move. The earth doesn't appear to move because it has a mass 10^22 greater than you so yes it accelerated but its so small that it is undetectable.