What I've learned so far, is that the three basic things I need to understand in order to take a quality photo are: ISO, shutter speed, and aperture. Not only do I need to understand them, but I need to learn to control them in order to get the results that I want.
Shutter speed: is basically how long the shutter is open or how quickly the photo is taken. The longer the shutter is open, the more light is let in. This also allows for movement in the photo which sometimes makes photos turn out blurry. Although sometimes that can be a desired effect, depending on the photo. A fast shutter speed will create a sharp image.
Aperture: determines your depth of field or how much is going to be seen in the photo. Do you want to be zoomed in on your subject or do you want to capture the whole scene (seeing lots of foreground and background)? Setting a "low aperture" focuses on your subject and gives you a shallow depth of field. Setting a "high aperture" lengthens the depth of field. The aperture controls how much the lens opens. Again we have to think about light. High aperture will let in more light, low aperture will let in less light. On a bright sunny day we want to make the lens smaller (think of the pupil in your eye) and in a darker scene you want to open up that lens to let more light in.
ISO: controls the sensitivity of the image sensor in the camera. High ISO means that the image sensor is working at full capacity, thus you don't need as much light. High ISO is good for low light situations. Shooting at a low ISO means the sensor is not running at full capacity so you have more flexibility with light. Apparently low ISO is great for a sunny day. ISO determines how much "grain" you will see in the photograph. I'm still not fully understanding ISO. I'm doing more research now.
http://www.canonoutsideofauto.ca/learn/photography-101.php
http://www.cnet.com/how-to/photography-101-learning-the-ropes-with-your-new-camera/