DP's and IAP's

Greetings fellow simpilots,
Although not totally new to sim flying, I'm confused about some real life info... Being from the Boston area, I've decided to "follow" the Red Sox around this baseball season. In an effort to do so as properly as I can, I've been going to the FAA site to get airport diagrams and the like. Question: What is the reason for multiple DP's? Is it related to the direction in which you plan to go once in the air? The runway you're using? I realize the IAP's are based on runways, but the DP's baffle me. How do you decide which one you need?
Thanks,
Jim
Although not totally new to sim flying, I'm confused about some real life info... Being from the Boston area, I've decided to "follow" the Red Sox around this baseball season. In an effort to do so as properly as I can, I've been going to the FAA site to get airport diagrams and the like. Question: What is the reason for multiple DP's? Is it related to the direction in which you plan to go once in the air? The runway you're using? I realize the IAP's are based on runways, but the DP's baffle me. How do you decide which one you need?
Thanks,
Jim