Snapshots are only available on Supporter accounts.
Snapshots are copies of your home directory. There is one snapshot for each day of the week, for a total of 7 copies. This way you can recover files you accidentaly removed from the past 7 days.
You can access the snapshots via ~/.zfs/snapshot/ (.zfs is a hidden directory and will not show up in the directory listing)
There are also daily remote Backups.