1st of all, a RAW file is a "digital negative". Everything is "0", except for the exposure(shutter speed and aperture setting) is what you set during u take the shot. Like film. But for film its a different story, there's already a setting inside it, that's why you see certain film produce different quality and style of pictures.

And Adobe Lightroom is a raw editing software. Where you edit the raw files, in Lightroom, you can edit the brightness and contrast of the image without much loss of quality. You can also edit the curves, saturation... almost everything. Because my rule is to get the most out of your shots - I always shoot in RAW. And the best thing here is the setting you made wont affect the original raw file, so once you're done with editing, you convert the image into JPEG while keeping the original raw file. Get it?

There's much debate on RAW vs JPEG going around. But I stand my ground on shooting raw. For using lightroom for editing your raws, its like having your own digital darkroom. Like the old days where people used the darkroom to give special effects on films.

Here's a simple RAW vs JPEG link
http://digital-photography-school.com/blog/raw-vs-jpeg/

Read on