JPEG with Lightroom 4.3?
Lightroom will work with just about any image file format; RAW, DNG, JPG, TIFF, PNG, etc.
All editing in Lightroom is non-destructive, using a text list of changes to the images instead of making actual changes to the image. For RAW files the text list is in a sidecar XMP file. With other formats it is added to the file but the actual image isn't changed.
I recommend you try the following. Take a photo outdoors in sunlight. If possible set your camera to store both a JPG and a RAW image file. If not, switch between the two formats and take the same image.
Import the two images into Lightroom. Now go to work on the RAW image. You will find you can recover more highlight and shadow details from the RAW image than you can see or recover in the JPG image. You will also find that you can increase the exposure of underexposed RAW files by as much as 2 stops without causing a big loss of quality, something that is impossible with JPG files.
These are examples of how the larger 12-bits to 14-bits dynamic range of RAW files, instead of 8-bit JPG files, can help your photography.
I suggest you start with these free Lightroom video tutorials.
Scott Kelby's book is good but here are some more good written references.
Living and loving it in Bangkok, Thailand. Canon 7D - See the gear list for the rest.