There is a large patch of color on the left. There are six sliders on the right. The top three represent the RGB color values for the color patch. The bottom three represent the HSV color values for the same color. You can use the sliders to adjust the color. Note that the sliders are not independent! Changing an RGB slider can force the HSV sliders to change; changing an HSV slider can force the RGB sliders to change.
(Note: Change the value on a slider by dragging the tab or by clicking in the bar.)
Some things to try: Check the 8 colors that that you can get by letting Red, Green, and Blue equal 0 or 1. Try other settings on the RGB sliders. Set Saturation and Value to 1 and slowly drag the Hue slider; note how the RGB sliders change. Also try dragging the Hue slider with Saturation and Value set to values other than 1. Set Saturation to 0 and drag the Value slider; this gives shades of gray, and the Hue slider is irrelevant in this case.