how do I back up my mac on a seagate one touch hdd?

Apple provides Time Machine, although that's not necessarily a bootable backup where one can just use it immediately. It should be possible to boot into basic utilities.

I've used Carbon Copy Cloner and Super Duper. They work better than Disk Utility's Restore feature because it's usually bootable and can make incremental backups where it doesn't just start over with a clean copy every time. There are also little things that cloning software does better, including being able to schedule regular backups. Disk Utility is purely manually selected for copying.

Follow the instructions in the Related Article above, or use the Disk Utility's Restore feature, or a product such as Carbon Copy Cloner or SuperDuper.

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