A content type is a 'type of content' (this could be an Excel document, a folder, an image, a document set, a web page, an item and so on - all things that can be saved in to a List or Document Library in Sharepoint.
If you do not 'allow management of content types' the document library will revert to 'default settings'. For me, in my SharePoint 2013 system, the default settings for a document library would be a single document type - either Word or Excel.
I think you need to see what kind of content types you have in your list - are there 5? One each for Word, Excel, PP, One Note and folder? If so, you should be able to set Folder to 'hidden' or even delete it from your document library. This way, you can keep content types enabled, so users can choose from the remaining 4 content types.
Here's how to get to the content type settings:
In my example I have 4 content types
If I select the document content type - I can see which template the document content type is using
As we see here, it is defaulted to use a .dotx - the 'tx' means it is a template, the '.do' part comes from .doc (Word doc).
I hope this helps a bit