Dropbox is a cloud storage service that allows users to access and share files across multiple devices. The document provides step-by-step instructions for setting up a Dropbox account, installing the Dropbox application on various operating systems like Windows, Mac, Linux, and mobile devices. It also explains how to upload, download, and share files on Dropbox. Additionally, it outlines steps to earn 250MB of additional storage space on Dropbox by completing tasks like taking a product tour, installing Dropbox on multiple devices, sharing folders, and inviting friends.