This is a 'File Cabinet' page, which is used for organising files! You can create folders and put the files underneath them.

This type of page is one of the options given when you create a new page. To see the other types of page that can be created select 'Types of Page' from the menu.

Files are simply uploaded from your computer by pressing the 'Add File' button that is visible when you are logged in as an invited 'Owner' or 'Collaborator' of the site.

Folders and files are presented in strict numeric / alphabetic order. When you are adding files this does not seem to be the case but, when the page next displays, you will find that the files have been re-organised.

 At the time of writing the folders cannot be collapsed  - I hope that Google will add this capability soon!