- On your iPhone or iPad, go to Settings > [your name] > iCloud > iCloud Backup.
- Turn on iCloud Backup.
That’s it. You can read there that backups will occur when the device is “connected to power, locked, and on Wi-Fi.”
If Backups are already on, the screen should show a “Last successful backup” at least within the last day. If it doesn’t, tap Back Up Now.
More info, for those interested:
Almost every normally used device needs more room to backup and store photos than the 5 GB that Apple includes with every free iCloud plan. Fret not: you can buy more iCloud Storage.
Many, many Mac users assume that iCloud backs up their Macs. It absolutely, categorically does not.
Every Mac or PC user should have a cloud-backup service such as Backblaze. Individually owned computers can use the Personal Backup product, while any owned by an organization can be under the Business Backup plan. [Those are affiliate links.]
Businesses might have their mobile devices signed into iCloud accounts under the user’s organizational email address. The user should know that the organization owns every bit of information on that device.