By Apple, Face ID is merged with Passcode in the Settings section. It looks not much different from the Touch ID.
The top is the Face ID usage option. There to open iPhone, purchase content in iTunes and App Store and fill in password in Safari.
For setting Face ID users simply press Enroll Face. Instantly a face icon will appear, then press Get Started to start scanning. Users are asked to place a face on a city that is already available. Then move the head slowly to the perfect circle.
When completed the application will inform you that Face ID scanning is complete. Press Continue to go back to the beginning.