Thank heavens the "top side" of the primer is rough, compared to the bottom side or primer flip trays wouldn't work.
It took me a little while to understand the geometry of a "flip" and that the tray had a lid so you could turn the whole assembly 180° after they were all shiny side down.
As you shake the tray, the rough side of the primer catches in the grooves of the tray, forcing the primer to flip. The shiny side doesn't catch.
To load a primer tube for many presses, the primers have to be shiny side up. The tube is inverted when the primers are dumped into the primer magazine on the press, and now they are shiny side down again, which is the correct orientation for repriming.
The first time I tried to do this, I did it with the lid on. Seemed nice and neat to me. I didn't want to spill any when I was shaking them. Well, there isn't enough clearance for the primers to flip when the lid is on.
Reloading involves lots of details. These forums are a tremendous resource, and are a wonderful addition to printed manuals.
Good luck.