What is ISO?
ISO is what allows you to take pictures in low light.
In a nutshell it basically is a measure of your digital sensor’s sensitivity to light. The higher the number, the more sensitive to light your sensor becomes.
How Does ISO Affect Your Images?
So if ISO determines how sensitive your sensor is to light, and your sensor records the light, then that sensitivity of the sensor is basically going to determine how bright your image will be.
What is Digital Noise?
"Film is composed of lots of little circles that make up the GRAIN of the film. Digital photography is similar, except for that our little circles aren’t circles at all, they’re squares. . . a gazillion little squares that come together to create an image. Sometimes those little squares in the image become slightly visible and this is referred to as NOISE." -Natalie Norton
What Does ISO Have To Do With Digital Noise?
Simple, the higher the ISO the more digital noise you will see.
Video
Here is a video I found on Youtube that helped me out when I got started.
http://www.about.me/jacobaddotta
