I don't think this is a condescending thread at all, I think it makes a very important point but let's not just yell at newbs. Let's talk about Why.
I'm going into my third season and I continue to refine my Understanding of The Ratings. YES it's the most important thing because it affects everything else you do.
But I can't find a Book on The Ratings. If you read enough of these threads you won't find one. Some things are obvious, like whether a player can hit for power, others are not, like why a player who looks like he should get hitters out does not. And there is enough disagreement between writers of these threads over how players work that you can't just write a Book.
I found a Mentor before I even started playing. He helped me with the mechanics of the game, but he never really said "look for this type of player or that type." I haven't really asked him much about The Ratings, because it's what you have to figure out for yourself. Three seasons in and I'm still going.
Understanding The Ratings is important because it doesn't just help you find good players, it defines how YOU VALUE players. And before you learn to do that, you can make mistakes like these which I have:
1/ Signing what only looks like a good player to a contract he is not worth. This ties up your money, maybe for several seasons. It may block roster positions from your prospects as well. You may wonder why other owners did not pursue this player. Later you find out that you can easily pick up cheap talent on the waiver wire. You overpaid for a replacement level player.
2/ As eastonest said, making a player available to the rest of the league through Rule V or Waivers, who you did not realize is more valuable to others than you thought.
3/ Trading a true prospect for replacement level talent - the classic Trade Rape. (I didn't do this, but I had an offer come in once that I realized right away was a setup. Not that I'm smart, it was kinda blatant.)
4/ Overvaluing those ratings which don't actually affect on-field performance. This is where ghengisxcon's point comes in, those ratings inflate a player's Overall without helping him hit or pitch any more effectively.
So yeah, it's all about understanding the ratings. Like Mike says, you have to take your time doing it. Don't get all horny to play with the new toy, watch it and figure out how it works and how it doesn't.