Your foreground color needs to be white and you have to select the gradient in the first row, 2nd from the left.
just select the second gradient on the top row from the left and make the color white instead of black. Just double click the color chooser on the bottom left
I think he asked HOW to get the editor up .. well you know the paint tool (Below the brushes tool) right click that and there would be a gradient tool. Click that and a bar near the top will change. Double click the gradient preview and the editor will show up
