This is the 6093rd most frequent Polish word.
andreas
The word "Andreas" is not a Polish word; it is a name derived from Greek, meaning "man" or "warrior."
In this sentence, 'Andreas' is used as a proper noun, the name of a person, serving as the subject of the sentence.
Andreas mieszka w Niemczech.
Andreas lives in Germany.
Here, 'Andreasa' (a declined form of 'Andreas') is a proper noun in the accusative case, referring to the person named Andreas as the object of the sentence.
Czy znasz Andreasa?
Do you know Andreas?
In this instance, 'z Andreasem' is a prepositional phrase where 'Andreas' is in the instrumental case, indicating the person with whom the action (speaking) occurred.