The Shared Files feature is not intended for that kind of use, it is for sharing files in a secure way so thet they can be protected by roles, nothing more, it is not intended as files for use in content in other features.
To link to a file in content like in the Html feature, you can use the link toolbar item in the wysywyg editor to browse the server and link to a file and you can upload files from there too. But those files are not protected by roles, if someone knows the url to the file they can download it, whereas with the Shared Files the download url checks the users roles before allowing the download if the Sharted Files is on a page protected by roles.
You could use Shared Files to share a file with your teacher if the Shared Files feature is on a public page just give him the url to the page. If its on a page protected by roles then your teacher would need to sign into your site and would need to be in the allowed role.
Hope that helps,
Joe