You can share a file or folder with someone via Dropbox by selecting the Share option and providing their email address. Follow these steps, depending on if you're using the Dropbox Sync App or Dropbox online:
|Dropbox Online||Dropbox Sync App|
Note: If you select to enter email address(es), you can add a personalized message about the contents and purpose of the file/folder you're sharing.
Issues may be seen when sharing/unsharing a file larger than 10GB or a folder with more than 10,000 files. See this page for more information.