Students and teachers can attach files to all content types (but not comments).

By default in this site (this setting can be changed), the link to the file attachment is only visible to logged in site users. This way, teachers may post materials "for one-time educational use only," and students may share drafts of texts which should not be public on the Internet. However, the files are public; only the links at the bottom of the page are hidden. If the link to a file is posted in a comment or other post, the file will be available to anyone.

You can

• enable/disable file attachments for individual content types at administer >> content management >> content types. Edit the content type you're interested in enabling or disabling for attachments. You can adjust this setting under the "Workflow Settings" expandable menu on the content type edit scree. There are additional settings you can experiment with.
  
• configure file size, number of files, and acceptable file types administer >> site configuration >> file uploads.
• control who can upload and view attached files at administer >> user management >> access control.