The benefit of using your camera in full manual mode is full creative control. Using your camera in aperture priority (normally shown as AV on your camera dial) or shutter priority (normally TV on your camera dial) are good ways to start getting your head around how the two relate to each-other and the effects they can have.
I found this on line a while ago and i think it is brilliant! It really helps you get your head around aperture, shutter speed and iso, how they effect your image and how they relate to each-other. I would definitely recommend you play around on it!
http://www.dryreading.com/camera/index.html
enjoy!