If you add a folder with subfolders in it, you will share the files in those folders but not the folders themselves. Unless off course they are zip-folders or rar-archives.
Someone please correct me if I'm wrong about this

Thats why it's probably the smartest thing to not select a folder with too many subfolders in it, as you later may add something that's not supposed to be shared by accident later

If you have a folder with subfolders in it that you want to share, it would probably be best to add all those folders instead and not the primary folder, at least if your PC isn't organized

note: I have browsed people on the network that are sharing their entire c: drive and that sure isn't safe