I know how the programs works, mainly. But when I save the file, in the add-on scenery folder it doesn't show up in FS.
Where are you putting the BGL file within the addon scenery folder?
You need to place it in the "Addon Scenery\scenery" folder or in the "scenery" folder of
the associated airport if you have that airport as an added scenery element.
If you just placed the file in the Addon Scenery folder itself, it won't work.
Paul