Dumb UI question on android.

[Bigpet]

If you go into the list view the button says "Pin" or "unpin" instead of "+" and "-" and what it does is pretty much add or remove the folder you are in to your "pinned folders". Your pinned folders always appear first in the list (you can observe this most clearly if you pin a folder and then repeatedly press on the "⇧"(up arrow) button)