Auto APN scans an internal Android APN database and selects an APN based on the SIM card's operator and country. If the first automatically selected APN doesn't work, it attempts to use the next existing APN from the database

APN (Access Point Name) is configurable network identifier used by a mobile device when connecting to a carrier

APN entered by the user

Authentication method that your GSM carrier uses to authenticate new connections on it's network

Your username that you would use to connect to your GSM carrier's network

Your password that you would use to connect to your GSM carrier's network

SIM card's PIN (Personal Identification Number) is a secret numeric password shared between a user and a system that can be used to authenticate the user