For example, by looking at the graphs above you should be able to tell how far the ball was thrown. So now we know the equations which relate position, velocity, and acceleration, and we know how to use graphs of these things vs. time to study motion. This is a key question for the physics of sports because many sports involve producing and controlling acceleration, either of the human body or other equipment. Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it. In the absence of external forces, objects in motion will stay in motion and objects at rest will stay at rest.
Forces come in pairs, equal in magnitude but opposite in direction.
The part about continuing to sit still makes sense, but the other part may be counter-intuitive. Your experience and intuition tell you that if you start something moving and then leave it alone it will not keep moving indefinitely but will eventually come to a stop. This is actually a good thing for this course because it is precisely these external forces which make sports so interesting, challenging, and entertaining. The 2nd Law is arguably the most important. The 1st Law tells you what happens if you leave something alone, but the 2nd Law tells you what happens if you push on it.