GradientEditor control looks by default like on the picture below. It allows to edit gradients visually. Left mouse button click select gradient point and also add new one if clicked on area free from other points. Right mouse button deletes clicked point. You may drag and drop points by mouse. To create a full fatured gradient editor you need also to use another controls and probably forms as well. You may look at gradient editing form in the Standard Package to see how several controls togather with GradientEditor can be combined to create a full featured gradient editor.

Gradient editor control(widget)