You no longer use your fingerprint to unlock the iPhone. With the iPhone X, you look at the camera to use Face ID. This face unlock feature works in the dark, with or without glasses, no matter what your makeup status is and even with a new beard. Apple tested this to make sure that it can't be hacked with a photo or even with a hollywood style mask.
The technology uses the new TrueDepth camera and uses 30,000 invisible dots to map your face and allow you to use it as the best way to unlock your iPhone X. You use this to pay with Apple Pay by double clicking the power button and then glancing at your phone before you pay. You must give your phone some attention for it to unlock, it will not unlock without the intent.
From a security standpoint Apple says there is a 1 in 1,000,000 chance that someone with a similar face can unlock it compared to a 1 in 50,000 change with Touch ID. The system will continue to learn your face every time you use it to improve the experience over time. When you aren't looking at the iPhone X it shows that there is a new Message, but once you look at it and it is unlocked you can see the content of the messages.