Wow.........this could be a guide that would take many pages.  To make this point quickly...the golf ball needs to be fitted to your swing just like shaft on your driver. 

If you are someone who hits the ball high, and you want a lower flight, you can change the ball you use to achieve this result.  If you hit the ball straight, there are balls just for that.  If you like shaping shots, there are golf balls for that too.  Why do you think Titleist makes a ProV1 and a ProV1x?  The same goes with Callaway.  Golf balls are made like drivers, they help you get better results off poor swings.  Balls are made to help the "slicer" hit less of a slice.  Different balls product various spin rates, and the spin rates effect the ball flight.

Again.....learn about the golf ball.  If you are simply playing to play the ball doesn't matter.  If you are playing and trying to improve, to get the most out of your game, learn about the ball and how it will effect your game.

More expensive golf balls don't mean you will get better results.  Better golf balls are made for better golfers, and golfers who want a very specific result. 

If you simply hit the ball and hope for the best, don't waste your money.  If you don't hit the ball consistantly and produce all kinds of ball flights, don't waste your money on expensive golf balls.  But if you do have some control and want more out of your ball, learn about them first.  There are low price, mid price, and high price golf  balls.  I am a single handicap golfer and the balls I used during my two lowest rounds where Titleist NXT and Titleist DT Solo. 

One more thing, some balls are hard and some are softer.  This is purely for your own preference.  I light a softer feeling golf ball, so that is what I go with.