As I have mentioned before there are three different camera settings on your DSLR that effect exposure including ISO, Shutter Speed, and Aperture. Getting into all three at once would be daunting so lets start with ISO!
A good way to think of ISO is to say that it is a measure of your camera's sensitivity to light. Therefore a lower ISO means that your camera is not as sensitive to light and can handle a bright, sunny day. A higher ISO means that your camera is more sensitive to light and can tolerate low light, maybe a dark room.
If you think of how your own eyes adjust to light, it may help you remember how to set your ISO. For example, on a bright sunny day you wish your eyes were not as sensitive to light right? Right! In a dark room, you wish you could see in the dark or that your eyes were more sensitive to light, right? Right! And of course, your pupils do actually get bigger and smaller to try and adjust, right? Right! On a bright sunny day your pupils get smaller, and in a dark room, they dilate or get bigger just like your ISO! Cool right? Right!! Ok, ok, I'll stop doing that now...
Anyways, here is an example from our outdoor patio furniture on an overcast day:
While keeping my other camera settings the same, I increased my ISO with every photograph:
You can see that increasing the camera's sensitivity or ISO while keeping all other settings the same, increased the image's exposure. In these lighting conditions I probably would have used ISO 320 or the second image's settings.
I think that is enough information for one day! If you want to play with your ISO, feel free to do what I did and start at your camera's lowest setting for ISO and increase it while keeping all other settings the same. Next week I'll add some tips/tricks/suggestions regarding ISO.