Follow the headline link, then:

• Click on each of the 4 color wells to set your gradient colors
• Drag the little squares in the left image to set your gradient starting positions
• Drag the squares in the right image to set the end positions

Rinse. Repeat. Export if you create something you like. Cmd-Z to undo. Shift-Cmd-Z to redo.

Have fun. Pass it along.