Adjustment layer
An adjustment layer applies a color or tone edit as a separate layer on top of your image, without changing the pixels beneath it. Think curves, levels or hue/saturation. You can always tweak or discard the setting later.
Adjustment layers are the non-destructive way to color and correct in Photoshop. Click the half-black-white circle in the layers panel and pick Curves or Levels, for example. Every adjustment layer comes with a layer mask, so you can paint the effect in or out locally. Tip: stack several adjustment layers for separate, easily adjustable steps instead of doing everything at once.
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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.