Dodge and Burn are tools on Photoshop that you can use to lighten and smooth areas that are lighter, or to darken shadows, or mess with in between tones. It's pretty simple, if you have Photoshop I'd advice just messing around with it. Select the tool, and use it like a paintbrush over the areas you want to change the exposure on. I'd also suggest going up and lowering the exposure slide bar thingy to something pretty low, like between 5 and 15. This gives you maximum control.