Mask opacity affects at the intensity of the selection, if you use 0% everything is un selected and there is no yellow area, as everything is unselected.
You have the selection inverted it seems, and everything is yellos, selected so it seems your selection is not selecting anything.
I usuallly do not use the left menu for selections, just when I need to delete a figure or something.
Usually you create the selection in the right menu.
But you can create it in the left an select one of the figures created to be applied to a module, they are the same, at the left you see al figures created for any module and grouped for figures used in a module.
It seems a bit confuse, I know.