Dodge & burn
Dodge & burn is selectively lightening and darkening parts of your image to emphasize shape and depth. Dodging lightens, burning darkens. In Photoshop you do this most cleanly on a separate grey layer, not with the tools themselves.
The built-in dodge and burn tools work directly on the pixels and are destructive, so better avoid them. Instead, make a new layer filled with 50% grey, set it to Soft Light or Overlay and paint with a soft black-and-white brush. That lets you sculpt light on skin, in landscapes or on products with full control and fully reversible. Tip: use a low brush opacity and build up calmly, so it stays natural.
Read also the in-depth explanation: Dodge & burn explained.
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.