How to back up data on a 2015 MacBook Air before regifting?

Some additional detail FYI:

Backing up a Mac:

https://support.apple.com/en-us/102307

And to properly wipe your Mac and prepare it to be re-utilized by someone else:

https://support.apple.com/en-us/102773

Not carefully following the above steps may:

1) Leak your PII, or

2) Ihibit any subsequent owner from even setting-up the Mac as their own.

How to Back Up and Prepare Your 2015 MacBook Air for Regifting

Your 2015 MacBook Air should make a lovely gift, particularly since it has been lightly used and is still working well. Before passing it along, it's important to back up your personal information, sign out of your accounts and restore the computer to a clean setup screen.

Follow these steps in order.

The easiest option is to use an external hard drive.

1. Connect an external hard drive to your MacBook Air.
2. Open Finder and locate the external drive.
3. Copy your Documents, Desktop, Downloads, Pictures and other important files.
4. If you use the Photos app, remember to copy your Photos Library.
5. Open a few copied files to confirm everything transferred correctly.

Alternatively, use Time Machine:

1. Connect your external hard drive.
2. Open Apple menu () >> System Preferences >> Time Machine.
3. Select your external drive.
4. Start the backup and wait until it finishes.

You can also use iCloud, but remember that syncing is not a substitute for a separate backup.

Apple’s guide: Back up your Mac with Time Machine.

Important: Don't erase the Mac until you've checked that your backup is complete.

Once your backup is safe:

• iCloud: System Preferences >> iCloud >> Sign Out. On Catalina or later, use Apple ID >> Overview >> Sign Out.
• Messages: Open Messages >> Preferences >> iMessage >> Sign Out.
• iTunes: If applicable, open iTunes >> Account >> Authorizations >> Deauthorize This Computer.

Apple’s guide: What to do before you give away your Mac.

Erase the MacBook Air

The 2015 MacBook Air does not support Apple's newer Erase All Content and Settings feature. You'll need to use macOS Recovery.

To access Recovery:

1. Connect the Mac to its power adapter.
2. Restart the computer.
3. Immediately hold Command (⌘) + R.
4. Continue holding until the Apple logo or spinning globe appears.
5. Wait for the macOS Utilities screen.

To erase the internal drive:

1. Select Disk Utility >> Continue.
2. Select View >> Show All Devices, if necessary.
3. Locate the internal drive, usually called Macintosh HD.
4. Select the appropriate drive or volume and click Erase.
5. Use these settings where available:

• Name: Macintosh HD
• Format: APFS, if supported by the Recovery environment.
• Scheme: GUID Partition Map, if shown for the physical drive

If offered, use Erase Volume Group for the Macintosh HD volume group.

1. Confirm and quit Disk Utility when finished.

To reinstall macOS:

1. Return to macOS Utilities.
2. Select Reinstall macOS.
3. Follow the instructions.
4. Choose Macintosh HD as the destination.
5. Keep the Mac connected to power and Wi-Fi until installation finishes.

Apple’s guide: Erase and reinstall macOS.

Prepare the Mac for its new owner

When installation finishes, the Mac should display the Welcome or Setup Assistant screen.

Don't enter your own Apple ID or personal information.

1. Press Command (⌘) + Q.
2. Select Shut Down if prompted.
3. Leave the Mac switched off.

The recipient can complete the initial setup using their own details.

For additional assistance, Apple provides these support guides:

Start up from macOS Recovery.

If you can't back up using Time Machine.

Use Time Machine with an external drive; on this 2015 Air, open System Preferences, choose Time Machine, then select the drive. Let it finish, then open the backup and check a few important files before wiping anything. After that, sign out of iCloud and erase and reinstall macOS from Recovery before handing it over.