Back up your Mac with Time Machine
Time Machine is a very simple tool in Mac OS X that can prevent the heartbreak of losing all of your important files. Time Machine is a great program that runs without you worrying about it.
After initial setup, all you need to do is make sure the hard drive is connected or that your Time Capsule is running. Time Machine will keep hourly backups for the last day, daily backups for the past month, and weekly backups for everything older than a month. You can backup for years depending on how many files you keep.