Levels (Photoshop)
With Levels you set your image's black point, white point and midtones in Photoshop via three sliders under the histogram. Move black and white inward for more contrast and the middle one for brightness. It is a fast, clear way to get your tonal range in order.
Add Levels as an adjustment layer and drag the outer sliders to where the histogram begins and ends, so you use the full tonal range. The middle slider lightens or darkens the image without shifting black and white. Per channel you can also correct color casts, like a too-blue shadow. Tip: for nuanced work reach for Curves, Levels is mainly strong for a quick base correction.
Read also the in-depth explanation: Levels (Photoshop) 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.