Dropbox for Mac is a Web-based storage location that syncs with specified files or folders on your Mac, allowing you to access them from anywhere. If you have two or more machines using the same Dropbox, changes to a Dropbox-tagged file will be synced on the other devices. Working across Mac, Linux, and Windows, Dropbox for Mac lets you access files even when miles away from your main machine (and even when its off).
To use Dropbox for Mac you need an account, although setting one up is easy. A free account is available that lets you sync 2GB. The Pro version costs $9.99 a month and supports over 100GB, while the Team version lets you sync 1TB (you get more space on each plan by referring new customers to Dropbox). To use Dropbox for Mac, a folder is created into which you copy folders and files (or pointers to files), and those are then synced with the Dropbox server. Obviously, you need an Internet connection to maintain the concurrency of those files, but any updates are synced as soon as you save. To access those files from another device, you install the Dropbox software and log in to your account. The files on the server are synced to your local device.
We've used Dropbox for Windows for quite a while now, and Dropbox for Mac provides a Mac client that lets us move our Office files around regardless of the laptop we're carrying. Once set up, Dropbox for Mac works cleanly and in background. We use it to access work files from home, and vice versa. In almost a year of use, we've never had an issue with Dropbox.