and you'll find that you won't get the 'default.html' problem any more. You had somehow acquired both an index.html and a default.html file - both identical - so I've deleted the default.html
The reason you're getting such odd urls on some of the pages is that you seem to be creating folders for each subject, and putting html pages (plus images) in every folder. That isn't necessary. Just create the whole site in NOF, and publish from within NOF - it will sort out the server-side file heirarchy for you automatically. You don't need to name your homepage index.html - NOF will do all that, once you've created the site architecture, and published from NOF.
In an ideal world you'll have all the images for the whole site in one folder, and all the html files will be together, in the root of the server space.
The problems you're getting are being caused because you are using NOF to design the site, but you're transferring the files into the server via a third-party FTP program, and you're creating the file structure yourself - don't so that until you are completely comfortable with how the server handles files, and how browsers display the urls.