Add your iPhone to Find My
Once you turn on the Find My iPhone setting, you can use the Find My 
(or Find My iPhone 
) app to locate and protect your iPhone if it’s ever lost or stolen. Activation Lock is also turned on.
Set up your iPhone
On your iPhone, do one of the following:
iOS 13 or later: Go to Settings > [your name] > Find My.
iOS 12 or earlier: Go to Settings > [your name] > iCloud > Find My iPhone.
If you’re asked to sign in, enter your Apple ID. If you don’t have one, tap “Don’t have an Apple ID or forgot it?,” then follow the instructions.
If Find My iPhone is turned off, turn it on.
Turn on any of the following:
Find My network (or Enable Offline Finding): On iOS 13 or later, the Find My network helps you find your device even if it’s not connected to a Wi-Fi or cellular network.
Send Last Location: If your iPhone is lost or stolen and its battery charge level becomes critically low, its location is sent to Apple automatically. When you use Find My (or Find My iPhone) to locate that device, you see where it was before its battery ran out of charge.
Tip: You can rename your iPhone to easily tell it apart from your other devices. See the Apple Support article Change the name of your iPhone, iPad, or iPod using your computer.
Set up other devices
To add your other devices or your family members’ devices to Find My, see Add your devices to Find My.
About Activation Lock
Activation Lock helps prevent anyone else from using your device if it’s ever lost or stolen. When you turn on Find My [device] on an iPhone, iPad, iPod touch, Mac, or Apple Watch, Activation Lock is turned on automatically.
With Activation Lock, your Apple ID and password are required before anyone can do the following:
Turn off the Find My [device] setting on your device
Sign out of iCloud on your device
Erase and reactivate your device
If you lose your device and remotely erase it using Find My (or Find My iPhone), Activation Lock remains on. Your Apple ID and password are required to reactivate the device. If you reset your device and erase all content and settings, Activation Lock is turned off.
For a Mac, Activation Lock is available for models with a T2 Security chip that have macOS 10.15 or later installed. For more information about Activation Lock, see the Apple Support articles Activation Lock for iPhone, iPad, and iPod touch, About Activation Lock on your Mac, and About Activation Lock on your Apple Watch.
Note: You should set up multiple methods of verifying your identity in case one of your devices is lost or stolen. See the Apple Support article Two-factor authentication for Apple ID.