If you keep all your work in your home directory here in CSE then backups are done automatically for you each night.
If you administer your own computer either here or at home then you need to arrange the backups yourself. If you have too much data to backup using floppy disks then backup hardware, like ZIP drives, is not very expensive. Remember to keep a copy of your backups off site in case you have a burglary, fire or flood.
If backup hardware simply isn't available but you do have an Internet connection then consider backing up to your ISP account or to your CSE account. This will give you an off site copy of your work. Remember that you cannot store an unlimited amount in your account--you do have a quota.
rsync is good for backing up remotely, and if you use your CSE account it will be backed up by us to tape automatically.
Don't email your hard-disk contents as a way of backing up!