I agree that the help is scanty. I agree that there needs to be a glyphs panel. I also think that if a feature is not present, the menu selections themselves need disabled else it will cause confusion.

The version of the font you downloaded from the site you did (I know from where that version came from) has the code related to discretionary ligatures removed. So while the glyphs are still present, there is no means of turning them on inside the font.

I have the legal version of that font and my screen shot was produced using XDP with merely turning on discretionary ligatures on the text.