OP, check out this link:
http://photography-on-the.net/forum/...d.php?t=414088
That forum is a AMAZING for Canon owners, and has a wealth of information. The article I posted may seem a bit intimidating at first, but give it a good read-through. It's also a good thing to have saved for future reference.
Basically (very basically) for exposure here's how it works...
Shutter Speed:
Longer shutter speed = more light coming into the camera. However, the longer the shutter speed, the more prone to "shake" the image is. Shake is caused from small movements of the camera while the picture is being taken. It will result in blurry pictures and wavy lines of light.
ISO:
Higher the number, the more light coming in to the camera. However, if you go too high, you increase the amount of "noise" in the shot, these are small spots on the picture making it appear grainy. If you're in a low-light situation, this is your best tool, as noise can be fixed (somewhat) in post processing, where as camera shake cannot be.
Aperture:
This is a little more tricky, and I think it's best explained in the article I posted.