Admins can add folders from the Archive. Simply select new folder, give the folder a name and then click on the plus sign. 

When you then create a user group, you can select a folder from the menu and assign access rights to the folder.  In the future, when for example creating signature invitations, you have to choose a folder where the document will be saved. If the user group in question lacks access rights to a folder, it also means that they cannot see the documents in it.