A connected external drive is not evidence that your Mac has a usable backup. The useful milestone is a completed Time Machine backup on the intended disk, with the password available when you need it.

Choose the destination before clicking Set Up

Use a separate external disk with enough capacity for backup history. Apple recommends a capacity of at least twice the Mac's storage. A disk that already holds your only copy of family photographs is a poor starting point: Time Machine may ask to erase it during setup.

Read the disk name and capacity carefully. If an erase prompt appears and the disk contains anything you need, cancel and protect that data elsewhere first. Naming the disk clearly and labelling its enclosure helps prevent later mix-ups with an ordinary file-transfer drive.

Finish setup and record the result

In macOS Ventura 13 or later, open System Settings, General, then Time Machine and add the backup disk. Earlier releases use a different settings layout. If you enable backup encryption, keep its password somewhere accessible independently of this Mac. Do not assume your Mac login password automatically unlocks the backup.

Allow the first backup to finish. Check the latest completed backup date in Time Machine rather than treating an active progress indicator as success. Record that date alongside the disk name in your own backup notes.

Before relying on the arrangement, browse the backup and confirm that a recent document you recognise appears. Plan a small restore test using a disposable practice file. Reconnect the disk regularly enough to cover the work you cannot afford to lose, and eject it before unplugging it. A backup left disconnected for weeks cannot contain yesterday's work.

Source: Apple's Time Machine setup guide.

For help with your Mac, contact AEPC in East Auckland or call 027 908 8880 to discuss your requirements.