This is the 611th most frequent Russian word.
николай
"Николай" is the Russian form of the name "Nicholas."
Here, 'Николай' is a proper noun, the name of a person, subject of the sentence.
Николай пришёл домой.
Nikolai came home.
'Николаем' is the instrumental case of the proper noun 'Николай' used after the verb познакомиться, meaning 'to get acquainted with'.
Я познакомился с Николаем сегодня утром.
I met Nikolai this morning.
'Николай' again functions as a proper noun here, being the subject performing the action of reading.