Pretty much since Photoshop came out it copied many of the tools and ways of film photography. One of these was the old Darkroom trick of Burning and Dodge. In the darkroom we would use our hands, arms, cardboard or pretty much anything we could get our hands on to hold back the light from the paper to make an area of the print lighter or concentrate the light to make something darker.
Photoshop carried this over with a couple of tools for burning (a hand with a circle in the fingers) to darken and something that looks like a black lollypop for dodging (makes things lighter). Unfortunately these tools never worked very well for a couple of reasons. When you used the Dodge tool would make a white haze and the Burn tool would sometimes cause color crossover as it darken. Plus you could only use them on an image layer which means if you make a mistake you could only correct it by going back in the History state or starting over.
With CS4 and CS5 Adobe did improve these tools with the Luminosity check box but you still can only use them on the image layer.
For me there is a better way which not only allows you more control but if you do make a mistake can be easily corrected.
Friday Quickie Tip. For any image what you will be doing is just Alt (Option for Mac) click on the new layer icon in the Layer Pallet. (That square with the corner turned up next to the trash can) This will bring up the New Layer Box where you can change the name of the layer to Burn and Dodge, Change the Mode to Overlay, and when the little box appears that says Fill with 50% Neutral Gray click to check it. Then Click OK. (To save time in the future make this an Action)
So now you will have new layer filled with gray but not having any change to the image. This is because the shade of gray is invisible to image just like a blank layer. However now when you paint on it with Brush Tool and black and white you are doing the same effects as burning and dodging. Take the brush tool, reduce the opacity of it to about 12% and with a soft edge brush you are adding depth and highlights to any image.
So if you make a mistake just paint it out with the opposite color. You can paint over the same spot a few times to add to your brush stokes and build up the effect. Want to reduce the effect just reduce the opacity of this layer. Looking for a different effect change the mode to Soft Light for an even more gentle effect. Want to bump it up use Vivid Light.
Burning and Dodging will help images that seem a little flat because of too much light. Remember do not fear the shadows and highlights. That is what give an image depth.