A folder allows a teacher to display several course resources together. The resources may be of different types and they may be uploaded in one go, as a zipped folder which is then unzipped, or they may be added one at a time to an empty folder on the course page.
Video (click on the green rectangle icon in the lower right hand corner to view in Full screen):
Using a folder to display resources is neater than displaying files one by one in a list. It takes up less space on the course page. (However, the folder settings allow for the files to be displayed on the course page if required.)
Content derived from : https://docs.moodle.org/31/en/Folder_resource