Divide each channel by 255. Value is the largest channel. Saturation is the difference between the largest and smallest channel divided by the largest. Hue is the angle on the color wheel.
Example: rgb(255, 87, 51) is hsv(11, 80%, 100%).
HSV is also called HSB (hue, saturation, brightness). Design tools such as Photoshop and many color pickers use it because it matches how people choose a color: pick a hue, then how vivid and how bright it is.
No. They share the same hue, but saturation and the third value are calculated differently.
It is the brightness of the color, from 0 (black) to 100 percent (full brightness).