Dropbox is not strictly a backup in the traditional sense of saving everything. What it does is synchronise a folder (and subfolders) to the cloud, and from the cloud to any device you connect to it. You install it on your PC, Mac etc and it puts a sub folder in your
My Documents. Anything you save to this folder gets uploaded to their servers. If you then install it on a second PC every thing will get copied down again to that one, and changes made on either will get reflected to the other.
The cloud versions can be accessed from the web if you’re away from the PC, and it also retains a version history which is very handy when you accidentally overwrite something
Because of data usage on a phone it works slightly differently. The dropbox app will show you the file names, folders etc but it doesn’t download anything till you actually click on it. This does mean you can in theory have a drop box account with 25GB on it but only 10GB of free space on your phone because all the files won’t be there till you ask for them, though each time you do download one you’ll eat up space.
You
can automate the syncing on your phone if you want using a 3rd party app called
folder sync lite. This is a little complicated to set up because it’s quite flexible option wise. It will allow you for instance to automate a one way sync of a dropbox folder called
current favourite tunes to a phone folder called music and only synchronise when connected via wifi