This is the 7811th most frequent Russian word.
итальянец
Italian man.
Here, 'итальянец' is a noun indicating a male individual of Italian nationality.
Этот итальянец готовит вкусные блюда.
This Italian man cooks delicious dishes.
In this usage, 'итальянца' is the genitive case form of 'итальянец', showing possession or relation.
Книга о путешествиях итальянца по России очень интересная.
The book about the travels of the Italian man in Russia is very interesting.
Here, 'итальянца' is the accusative case of 'итальянец', functioning as the direct object of the sentence.