The HSL / Grayscale tab sheet offers 32 sliders and one check box for switching between color adjustment or creating a black & white effect.
Preset
The Preset combo box at the top offers many creative presets to choose from. The Default option resets all sliders to zero and deactivates the effect that is produced by these controls.
Convert to Grayscale
If the Convert to Grayscale check box is not active you can see Hue, Saturation and Luminance tab sheets, otherwise a Grayscale Mix tab sheet appears and the image is converted to black and white. Each of the four tab sheets contains eight sliders with the same names. The value of each slider ranges from -100 to 100.
In Camera Raw 10.3 and higher there are "Color" and "Black & White" radio button at the top of the Basic tab sheet. They basically have the same functionality as the Convert to Grayscale check box. So if you activate the "Black & White" ratio button, the Convert to Grayscale check box is automatically activated. And if you activate the "Color" ratio button, the Convert to Grayscale check box is automatically deactivated.
Hue, Saturation &
Luminance
The sliders on the Hue tab sheet let you shift the hue of certain colors within a limited range. For example you can change red to something between magenta and orange, orange to something between red and yellow and so on. So you can only change each of the eight colors to the neighbor colors on the color spectrum. You can use this for subtle color corrections, bringing out certain colors as well as wild color effects. It is your choice.
The Saturation tab sheets offers the same color sliders (Reds to Magentas), but lets you decrease or increase the saturation of each color. With the help of these sliders you can fade certain colors and emphasize other colors.
The Luminance sliders lets you increase or decrease the luminance (meaning brightness) of each of the eight color areas. Making certain color areas darker and others brighter can subtly increase the contrast of the image. But it can also help to selectively enhance shadows or highlight areas in case they contain different color tones.
Grayscale Mix
Once you have the Convert to Grayscale check box activated you already see the image in black and white. The eight sliders let you change the brightness of areas that had a certain color in the original image. For example you can decide to make orange and green areas, e.g. skin and trees, brighter and blue areas, e.g. the sky, darker in the black and white image. Using different slider values lets you create a more impressive grayscale effect.