Creating a new folder just need you to navigate to the folder where you want a new folder in the filemanager window > right click the blank space and then choose New Folder:
Now you can go inside the new folder you created and right click > Upload Files (or just drag the files in this file manager window):
To assign this new folder to a user, you can go to the users page under the filemanager menu, find the user in the list and click Folders infront of it, this will show you all the folders that has been assigned to that user:
You can now assign that new folder (DMAX in this case) to this user with read/write access. Read/Write access will let the user upload and edit files, if you choose read only, it will just let the user download and read files.
Now you can use the shortcode
[filemanager foldername="*"] in any page to show this user (or any other users) all the folders that has been assigned to them. Here is an example:
You can now see all the folders that has been assigned to this user in the front-end of this page: