Dropbox is a software that allow you to put your files in a remote server under the protection of your account.
It is a storage where you can access with your devices: there is a software for your pc, an app for your mobile or you can use the Dropbox website to navigate your files.
You can also share files in the Public directory giving links to your friends.
Very usefull if you must work with a file in several devices (desktop - laptop).
Dropbox has 2 GB of free space for you: http://www.dropbox.com
There are many services like Dropbox:
Sugarsync - https://www.sugarsync.com/ : 5GB + 500MB for referral
MiniMedia - http://www.mimedia.com/ : 7GB
Skydrive - http://www.windowslive.it/skyDrive.aspx : 25GB
