Helmann,
Last year, a baseball newbie (he appropriately named himself "baseball-newbie") started a thread here that got quite a few responses from people who were willing and able to answer his questions about baseball. He was in the same situation as you: new to the sport as well as new to this simulation game. You might do well to follow this link and read through that thread. Just bear in mind that at that time we were talking about OOTP 2006 if there are any references to that game. Baseball, though, has not changed! Here is the link:
hits + at bats + BA + OBP = confusion