How can one understand people after having absorbed religious concepts online?

This is called firasah (physiognomy or intuitive insight), which is the ability to know inner states through outward signs. It has been narrated in the tradition: "Beware of the firasah of the believer, for he sees with the light of Allah." Firasah is proportionate to the strength of one's faith. If there is a deficiency in firasah, it may be due to hardness of heart or weakness of faith. The remedy for this is frequent recitation of the Qur'an.