Time Machine! Apple makes it so simple and easy to backup your important data. You'd be crazy not to take advantage of it!
How to Free Up Space Used By Time Machine’s Local Backups on Your Mac
How to transfer a Time Machine backup to another backup drive
How to delete old backup from Time Machine in Mac OS X
Mac Basics: Time Machine | http://support.apple.com/en-us/HT201250
Stop Spotlight from Indexing Time Machine Backup Volumes & External Drives
Time Machine Info--to save photos separate from backup...
Time Machine backs up all of your files to an external hard drive so that you can restore them later or see how they looked in the past.
A Time Machine Backup that has failed with a read only error is scary. But don't reset the backup drives file permissions, use this tip instead.
How to move Time Machine backups from one AirPort Time Capsule to another - Apple Support