So How Does it All Work Together?

Each of these settings can, and does have an effect on the other settings. For example, if you're shooting an indoor gymnastics meet and need to have a fast shutter speed to avoid motion blur, you may have to increase your ISO speed and open your aperture farther, so your sensor receives more light. Unfortunately, by doing this, you will be both reducing your depth of field, and increasing image noise - something you may have to settle for to get the shot. On the other hand, if you're shooting portraits of your children outside with plenty of natural light, you'll want to lower the ISO speed as much as you can, so there's less digital noise.

The main thing to keep in mind here is that the end result of all these settings is your exposure. This is simply how much light is hitting the sensor. An image is considered "over-exposed" if there is too much light, thus the resulting image is too bright and too washed out. An image is considered "under-exposed" if there isn't enough light which results in a image that has little detail and is too dark.