Sigil: City of Doors

I am curious as to how this works since I cannot seem to find the manual. Any ideas?

On your little DMFI toolbar, the bottom right next to SetDifficulty, you'll find a button with an icon that looks like a purple dude. When polymorphed, clicking that will bring up auxillary bars, including the polymorph one.

How do I use it though? When the little bar comes up, it is empty. How do you add stuff?

Stuff should just be in the bar if you've got abilities you can activate while polymorphed. Only a few things do though, like the racial Firre polymorphs and stuff like that. Fairly sure you can't add stuff, it's just for the bonus special abilities you get while polymorphed into select specific forms.