One of the problems with applying dodge and burn tools directly to the photo is that these actions change the original pixels irreversibly. For this reason some photographers only ever make dodging and burning changes on copies of the their photos, not the originals, but there is another way to achieve the same ends non-destructively and without the need for creating multiple copies.
The technique uses a special dodge and burn layer that sits above the picture and relies on the power of Layer Blend modes to darken and lighten the image. In fact the traditional dodge and burn tools are not used at all to achieve the outcome.
01 Start by creating a new blank layer above the image or background layer. Next rename the layer Dodge and Burn and change the Blend Mode of the layer to Soft Light. The lightening and darkening changes will be applied to this layer and the original pixels beneath will not be touched.
02 To burn in make sure that the new layer is active and then select the default colours for foreground (black) and background (white). Select a soft edged brush and reduce the opacity to between 20-30%. Start to paint in the bright areas of the image. The black paint combined with the Soft Light blend mode acts like a non-destructive burn in tool.
03 To lighten or dodge areas switch paint colours so that now the foreground colour is white and paint away as before. In this scenario the white paint and the Soft Light blend mode works like a non-destructive version of the dodge tool.
In Photoshop Elements: