Tutorial or video available for variable layer height tool in P 2.3?  

Tutorial or video available for variable layer height tool in P 2.3?

I was reading an interesting post about optimizing a print down from 8ish hours to under 3 - and various settings were tweaked along the way, each yielding a different print time difference.  A great post with lots of details - just the kind of thing I like about this forum.  One setting I saw is called variable layer height.  The post didn't specify much other than an additional gain by setting variable layer height.  So I went fishing in the prusa slicer and found the button on the top tool bar.  Good so far.

Clicking it exposes a small window with a couple of named settings next to shaded bars.  The bars make it clear that left click does X and right click does Y.  But I could not figure out WHAT to click in order to go farther with variable layer height.  Since I'm sure it's documented in a how-to somewhere, could someone point me in the right direction?  My clicking around taught me that the shape I wanted, but clicking on the shape in the window didn't cause any noticeable action or change - so I figure there is something I need to learn.