I have 10 dropbox invites and no friends. If you’d like some, post your email in this thread and i’ll send you one.
Dropbox is a “file cloud” service. Like XDrive back in the day, and Wua.la more recently. Your dropbox is a folder in My Documents, which you drag and drop files into. It works exactly like a normal folder, but anything you put into it is uploaded instantly to the dropbox file servers, so your files are online. As an example of what it can be used for, my wonderfully hilarious signature is hosted on my Dropbox. You get 2gib of space, so you can host isos and movies that you want to share between computers, or school files, whatever.
I also have Wua.la invites if you want some of those.