From a Home screen, tap Apps > Settings > Security & Screen Lock.
Tap Screen lock.
If presented with "This device does not have a Google account associated with it...", tap Add Google account now to setup an account before proceeding. To proceed without setting up a Google account, tap Continue.
If presented, enter the current PIN/password/pattern.
Tap Face Unlock.
Tap Set it up.
Position face within the provided area.
Hold still for several seconds to allow image capture.
From the 'Choose backup' lock screen, select one of the following options:
If presented, tap Next.
Draw an unlock pattern (connecting at least 4 dots) then tap Continue.
Re-draw your pattern then tap Confirm.
If presented, tap OK.
Enter a numeric PIN (at least 4 digits) then tap Continue.