A chrome book is primarily for browsing the internet and storing your 'stuff' in the cloud.
For example you create and store documents via Google Drive; you use GMail for your emails which are stored in the cloud; Picasa for your photos, Play Music for music
The advantages are the machine should be quick and theoretically you will never lose your 'stuff' if it is lost/stolen/dead.
The obvious disadvantage is that a Chrome Book is next to useless if you can't connect to the internet for any reason.
https://support.google.com/chromebook/answer/3265094?hl=en-GB