Week 11 Muddiest Point and Question

I have no muddiest point, but I have a question about Greenstone. How can I upload files into Greenstone? My understanding is that under the Gather tab, I can choose Local Filespace, choose a drive and file. When I try to drag and drop this file to the right, under Collection, nothing happens. Some students have expressed interest in dedicating some class time to a brief Greenstone tutorial about, for instance, uploading files. Is this possible?