How to Setting up Face ID
Pick your options
In Settings > Face ID & Passcode, set Face ID to unlock your iPhone, confirm Apple purchases, authorise Apple Pay transactions and/or enable access to items stored in iCloud Keychain or a third–party password app. Any options you turn off need your passcode instead.
Learn your face
To set up Face ID (if you didn’t do so when invited on starting up your new iPhone), tap Set Up Face ID, then Get Started, then roll your head in a circle as instructed so that the depth sensor can do its work. After doing this twice, tap Done. You’ll still need a passcode as a backup.
Ad another look
In iOS 12, there’s now an option to set up an alternate appearance. This is like adding another fingerprint in Touch ID, and is intended for people who sometimes wear glasses or headgear. Note that the only way to remove an appearance is to scroll down and tap Reset Face ID.
Face ID in action
Face ID will unlock your iPhone when you pick it up (if Settings > Display & Brightness > Raise to Wake is on) or after you tap to wake it. You can also use it for other purposes you set. By default, it needs eye contact; if you find it hesitant, turn off Require Attention for Face ID.