Cloud storage is like a PC hard disk, but it's located in the Internet. You can store your music, video, images, etc. in it and access them anywhere where Internet connection is available.
To begin using mySites cloud storage you need a mySites account, which you can create at www.mysites.com. Once you have an account, you can use it from Dazzboard's iGoogle gadget or Facebook application, just drag&drop content to the cloud.