The "Information" dialog contains useful information about the color values, selection dimensions and current position of the pointer in an image window. It can be a valuable source of instant information as you work on an image.
To open up the dialog, select Information from the View menu.
There are four sections in the dialog:
R G B in the top-left corner gives the respective values (between 0 and 255) for red, green and blue in any color that the pointer is currently passing over.
C M Y K in the top-right corner gives the respective percentage values for cyan, magenta, yellow and black in any color the pointer is currently passing over.
X Y in the bottom-left corner gives the coordinates in pixels (horizontal and vertical respectively) of the current pointer position.
W H in the bottom-right corner gives the width and height of a current selection, hence helping you to size selections accurately as you make or edit them.