If a folder has a "+" sign on it, then it contains subfolders and / or files. If a folder has no markings on it at all, then it is empty.
Click on a folder with a "+" on it to expand the folder and view its contents. Upon being opened, a folder's "+" indicator will change to a "-".
If there are any available files in the highlighted category they will appear listed to the right of the file navigation tree below. Click on the file name to view more information about the file and to access a "Download" link, which will allow you to view the document or to save it to your local computer.