New Segment Editor effect: Local threshold

Yes! But I don’t get it: pressing cmd+left click (I assume mouse left click) - where (in which window) and when should I press these buttons???

e.g if I use level tracing than I just need to left-click on the mouse and I immediately see the segmented area - however in local threshold the region is getting lighter and darker green constantly but if I press cmd+left click nothing happens…Bildschirmfoto 2020-06-25 um 21.54.49