Ack - hold a second. I notice you are using a Mac. You have posted your question in the Windows forum. Try the Mac forum. But I will leave this post up for any windows users who might find it useful.
Hello there Olivia,
Use the shift or Ctrl key and mouse together in the binder. For example, if I have three chapter folders with three scenes in each, I would hold the shift key down whilst selecting with mouse Click folder one with shift and mouse and then folder three. You should see all between them selected. This would then be displayed on the cork board showing the index cards for the folders and scenes for all the selected items.
Ctrl - hold it down and select each item. This will add them all to the same selection.