Keep in mind that:
Tap Security > Smart Lock.
If you don't see Smart Lock, try the following:
Whenever you turn on or wake the phone, it will search for your face and unlock the screen 
Show your face to the lock screen.
If it doesn't recognize you, it stays locked and displays one of these icons.
| Icon | How to unlock |
|---|---|
| Use your password, PIN, or pattern | |
| Use the fingerprint sensor |
If you're having trouble getting the phone to recognize your face:
Touch Security > Smart Lock.