When created a List(Lists can be documents, project task, e.t.c) in the Sharepoint, by default it will give the option Create Folder under New task under that list. For hiding the Create New Folder option, First, you should be owner to the site and then follow the following steps..
- Go to the List
- Click on Settings
- Select List Settings
- Click on Advanced Settings, Which is under genaral setting
- Check "NO" option for - Display "New Folder" command on the New menu?