What's the difference between RAW and JPEG files?

For the Nikon d3000… I want to know which is better to shoot in.

In digital camera terms, RAW is simply the raw information on the sensor--just a bunch of 1's and 0's. A jpeg is inherently a photographic file.

Or, put another way, RAW is simply film that has been exposed but not developed. Jpeg is film that has been developed in a set, standard way to make an image.

Because RAW has to be "processed" to make an image, it gives you more control over how the image ultimately comes out, because you can adjust things like color, contrast, saturation, sharpness, etc. With jpeg, because it's already undergone the fixed "development", it's much more limited with what you can do to adjust the image. This is because jpeg is "lossy," that is, it throws away data that it doesn't think is needed.

Example: Suppose you shoot in daylight but have the white balance set to indoor shooting. Your photos will come out blue. With RAW, no problem to fix, because you have the original data and you just change the white balance when processing the RAW file to make an image. By comparison, with jpeg, if the white balance is that far off, there's no way to fix it because the data to make the colors right has been thrown away during the process of creating the jpeg.

Thus, if you can always get it right, jpeg is fine. But if you want the maximum flexibility and quality and don't mind doing some computer work after taking the photo, RAW will give you more latitude.

Essentially, you can also think of it this way: your camera always shoots RAW. But if you have it set to jpeg, the camera will take that RAW file, process it in the camera, and save a jpeg to your memory card, discarding the RAW (usually, unless you save that too). If you have it set to RAW capture, then the camera saves the RAW and you do the work that the camera would be doing (converting it to a jpeg). The advantage of that is that you get control over the conversion factors to your liking, not the camera's internal choice