I assume your question is related to the cursor editor, because the "graphs" are only there. It shows how gradient color is interpolated between primary and secondary colors with distance (or angle in case of conical gradient). By default it goes from one color to the other, but you can make it go forth and back multiple times.
To use gradient, you must click the Gradient fill or Combined buttons in the panel. Not all tools can use gradient, but for example Rectangle can.
The gradient types differ in how they fill the area. You'll see.