There are two main ways to backup your Apple computer.
1. Use Time Machine to automatically backup. This is the Apple way – the easy way.
2. Manually backup your computer with some other software such as Super Duper or Carbon Copy Cloner.
Apple’s way (Time Machine) is a lot simpler. The big disadvantage is that the backup is not bootable. If your computer crashes you need to insert the original DVD and restore from at the Time Machine backup. This can take hours.
The second method takes a few steps longer to set up, but your backup will be bootable. That means if you plug your backup drive in hold down Option-Command-Shift-Delete during startup you can boot straight off your backup drive. In an emergency you can plug in your backup and be running from it under a minute. You can’t do this with Time Machine.
This article describes how to manually backing up using Super Duper. Carbon Copy Cloner and Super Duper are both paid apps. Super Duper has a free version which will do the job.