Time Machine

Every Mac user should use Time Machine to keep their data safe, or use a tool such as SuperDuper or Carbon Copy Cloner to maintain a clone of their startup disk. Also back up your files to a cloud service, such as Backblaze. Though Time Machine is straightforward to use, you can do more than plug in a drive and click OK to back up.

The Options button in Time Machine’s prefs gives you a way to define exclusions (if, say, you don’t want ‘rubbish’ like your Downloads folder to be backed up). Your external drives may appear in the list; remove them if you want changes to files stored on them to be backed up. Want rid of all backups of a file? Choose Enter Time Machine from Time Machine’s menu bar icon, browse to the file, then ≈- click it and choose Delete All Backups.