Print out this fact sheet from the American Dietetic Association to learn about food labels:
Shop Smart - Get the Facts on Food Labels
I also like the video below from monkeysee.com. A Registered Dietitian explains food labels in detail.
There are 8 segments, so make sure to click the "Next Segment" button after each video is finished. It will take you to the monkeysee.com site after you watch the first video.