Macs make automated backup childishly easy: simply plug in an external hard drive and OS X will ask whether you want to use it as a Time Machine disk. Say yes, and you’ll then get fully-automatic, hourly, versioned backups without doing anything further.
Unplug it to take your MacBook out & about, and it will catch up as soon as you return and plug it back in. Even easier, get a Time Capsule, and those backups take place over wifi, so you don’t even have to connect a drive.
But I’m a belt-and-braces chap. I like multiple backups, and I like one of those backups to be off-site. That way, if the house burns down, or a burglar takes both my Macs and my backup drives, I still have access to my data. Which is where online backup services come into play. Think of them as your backup of last resort.
iCloud, covered in my cloud storage roundup last week, already backs up quite a lot of your data – but nothing like all of it. The services covered here are ones that backup either your entire Mac, or a large proportion of it …