RAW, as the name suggests is not really a photo file format, rather it is the raw data captured by your camera’s image sensor. A RAW file contains much more data across a far wider dynamic range (dark to light tones) than can be seen on screen at any one time or printed. For that reason, it needs special software that comes with your camera to open, which permits quite large changes to things like exposure and colour saturation, without degrading image quality at all. Ideal to get the very best quality from your images.
TIFF is an image format which is not compressed, i.e. every pixel of an image is stored separately. For this reason, TIFF files are very large, but they can be saved as many times as you wish without degrading image quality. Ideal if you want to perform any post processing on your image.
JPG is an image format in which a compression algorithm is run on the pixel data to dramatically reduce file size. For this reason it is ideal to use to publish images to the web, or at larger resolutions, to get your prints done. However, each time a JPG is saved, image quality is reduced by a tiny amount. If this is performed repeatedly, these reductions are amplified, like taking a photocopy of a photocopy. Hence you should save a copy of your TIFF file as a JPG only when you have finished processing. And if you wish to make any changes, go back to your TIFF, work form there and then save another JPG.
But wait – my camera only shoots in JPG! Don’t worry, use JPG then – after all, 99% of all that matters in photography is in the initial composition.