Hi Sue, one of the good aspects of digital, is the exif info files saved with your picture. When you load a photo, go to file and click on it. Somewhere down the list you should see, "exif info". Click on that and it will give you all the info that is stored with your picture. Make of camera, time, date and most importantly, the exposure details. Shutter speed, apperture and iso settings. you can learn a lot from that. Judging what is wrong with the photo, and why. At first, it is worthwhile taking a set of pics at different settings, and seeing which ones work. The exif info can give you a better idea what settings to use next time in those conditions.
The next important tool, is the histogram. Shows you the spread of shades between white and black. Read the book to find out how to use it, because it is a photo saver. You can bring a dull photo to life. It will take too long to explain it here. Hope this helps in some small way.