One of three possibilities for user input appear in this window. The options are for setting the light direction, the object's location and the shadow color including its transparency. The particular option is determined from your choice in the Selection Panel to the right.
When setting the light color, note that the natural color of a shadow is one on the gray scale -- that is, the red, green and blue components have the same value. Thus, when you change one of the components in this window, the others will also change. Secondly, you can change the transparency of the color. You may first think that a semi-transparent shadow is not natural. Try casting a shadow on a table (or counter) that has glass or very thick acrylic coating on it. The underlying material of the table will appear through the shadow.
When setting the light direction, you can think of the coordinates as those of a point with the light going from that point towards the origin. For example, if we want the light rays to point more to the left and, in turn, the shadow move to the left, we increase the value of the x coordinate.
When setting the object's location, you may change anyone of the three coordinates, x, y or z.
As for any of our tutorials having a parameter input window, we can use either the mouse or the up and down arrow keys to change any of the selectable values that are initially drawn in green.