How to use NFC to open my door ?

You are missing the biggest pieces in this puzzle and that is the app and a digital key that needs to be issued to you by your company (employer), Hotel etc. You cannot just take the iPhone near a door because the lock will not magically open.

Axel F.

It will depend on the door control system. I assume you will need an app from the lock manufacturer to hold or install the electronic keys. The manufacturer will need to support iphone nfc.