The editing tools are found below the selecting tools on the tools panel. Naturally, they all have different functions related to editing an image. You can do simple procedures like draw or erase, or perform more complex tasks like dodging and burning -- manipulating the exposure of selected areas -- that will make for studio quality prints and creative visuals.
As with the Selection Tools, there are other tools with similar functions nested within each of the default Editing Tools on display. Remember, click and hold over any of the tools to see the variant options.
Dodging part of an image means that you are brightening up that part, whereas burning it means you are making it darker. In the image below, the area of grass above the dog has been dodged, and the area below him has been burned while the area by the hose has been left alone. See the difference?
These tools can be especially useful if you are cropping part of an image out and layering it on another image, merging the two, and you want to get rid of the "halo effect" -- the bright contrast around the perimeter of the cropped image -- and make the final result look pure.