You can share files with anyone, including people without Dropbox accounts, by sharing a link to any file or folder. You can send a shared link by email, Facebook, Twitter, instant message, social networks, wherever you want.
Shared links are view-only, and by default anyone with the link can view and download its contents.
Dropbox Professional and Dropbox Business customers can add passwords and expirations to shared links.
Sharing using shared folders
If you need to work with someone on files, you can create a shared folder. Files in shared folders sync between members’ Dropbox accounts, so each member of a shared folder needs a Dropbox account.