The Hue/Saturation command adjusts the hue (color), saturation (purity), and lightness of the entire image or of individual color components in an image.
Use the Hue slider to add special effects, to color a black and white image (like a sepia effect), or to change the range of colors in a portion of an image.
Use the Saturation slider to make colors more vivid or more muted. A good use of this adjustment would be to add a color punch to a landscape by adding saturation to all the colors, or to tone down a distracting color, like a vivid red sweater in a portrait.
Use the Lightness slider in conjunction with the other adjustments to lighten or darken a portion of an image. Take care not to use it on an entire image—this adjustment reduces the overall tonal range.