Well I know in the general sense but I mean when using the Android UI. Try this on the emulator -

On the home screen choose "Add"
Choose "Shortcut"
Choose "Folder"

So, a folder appears. A single tap shows a large empty window. What can you do with that? I though it might be a convenient way to organise other items, so with that window up did another Menu | Add | Bookmark and that just went to the main desktop. I can't seem to add anything to these folders!

You were so close!
When that empty folder is up, bring up the apps list and long press one. you can than drag it to the folder. So its a cool way to organise apps, links etc on your desktop.