No, not "file-sharing" as in illegal music downloads.
Rather, what happens if you want to share one file that is too big to email, or perhaps several files that don't fit as attachments to a single email. Or, it's how to share a file if your email is being cranky or strange.
Here's the link explaining how to share files easily: http://www.makeuseof.com/tag/dropbox-quickest-ways-share-file-si/. You'll find several different sites you can use. As with 99.9% of the stuff I mention on this blog, the file-sharing services are free for basic and highly-functional use. Some use a "freemium" model, charging for extraordinary volume or particular extra services; but you won't need to pay anything if you're in "just getting started" or "occasional user" modes.
Posted on my blog, of course.