http://www.TheArtofRetouching.com - This Adobe Photoshop CS5.5 tutorial covers the difference between using a RAW file format, and a JPG, or JPEG, file format. If you know the difference, you can easily skip this video. There are no secret surprises or revelations here. However, if you do not know the strengths and weaknesses of each, then by all means, watch and learn.
This Photoshop Tutorial is an overview of the RAW file format. No real detail is covered. Rather, this is a dip your feet in, and see why it is the choice of professional retouchers and photographers.
In short, JPG, or otherwise known as JPEG, is a lossy compression format. This means, that in order to keep the file size as small as possible, pixel data and other information is literally thrown away. Basically, if you have two very close shades of blue pixels next to each other, it will make one pixel the same as the other, and discard the extra information. The less information, the smaller file size.
RAW format, however, retains every little detail in such a way, that a file can be easily manipulated with a RAW processing program such as Adobe Photoshop's built in converter, Adobe Lightroom, Apple Aperture, or Phase One's Capture One.