Snapshots were available during the intro period but not after. Are those the "backup" option if I choose to add that on?

Yes, with backups enabled you have a standard set of backup slots (daily, and two prior weekly) that are filled automatically when backups run, plus a snapshot slot. You can take a new snapshot at any time, which then replaces any prior snapshot in the snapshot slot.

Without backups enabled, there are still ways to duplicate your disk images (to other images on the same Linode if you have space, or to another Linode if not) but they involve downtime during the cloning process.

(See also https://www.linode.com/backups/)

-- David