If an admin needs access to a user's files and folders they will need the user's explicit agreement to do so.
As the user, log into the web portal. Under the User Menu, click Settings. In Settings, go to the Settings tab.
Here, by default, 'Allow tenant administrator access to my files list' is unchecked.
An admin can edit the user on the web portal, go to the Storage tab and view the user storage. Here, the admin can see user's files/folders. However, it is read-only and the admin cannot open/download any file. They can only see the file/folder names.
If the user checks 'Allow tenant administrator access to my files content' under settings, when they view the user's data,the admin will have full control of a user's private files.