Objects have a natural resistance to changes in terms of motion. This resistance, called inertia, varies with the mass of the object itself. The larger the item is, the more force it takes to move the object, to stop it or to change its direction. For example, it's easier to stop a marble rolling along the floor than it is to stop a bowling ball. It's also important to remember that each object is motionless from its own frame of reference if it's not accelerating or changing its speed or direction. This explains why your body is pushed back against the seat of a car when the vehicle starts moving; your body attempts to stay still but because the car is moving, your body can't help but move as well as the car accelerates.
The Law of Acceleration is the most basic law of motion. You learn the equation associated with it before you learn anything else in physics: force equals mass times acceleration. This refers to both how much force or momentum an object has and the amount of force needed to accelerate it a certain amount. This law is different from the previous understanding. Aristotle's mechanics held that force needed to be constantly applied to maintain velocity. In fact, force is only required to change an object's velocity. In space, you can accelerate as much as you want then turn the engine off and coast along. When you do so, nothing will stop your motion.
The third law determines balance. For every force applied to an object, the object will apply an equal but opposite force in return. If you push a door, the door pushes you with the same force. This may seem like it would stop any movement at all, but friction, leverage and mass play a part as well. If you and a friend stand on an icy surface and push, you will both slide away from one another.
Newton's laws of motion apply for most of the matter you'll experience in everyday life, such as the second law. However, it doesn't work at high velocities, such as the speed of light. As you approach the speed of light, the force needed to accelerate increases. You would need an infinite force to accelerate to light speed, which means that light speed can never be reached.