This is the 1042nd most frequent Russian word.
мужчину
The word "мужчину" is the accusative singular form of "мужчина," meaning "man" in English.
'мужчину' is the accusative form of 'мужчина' and is used as the direct object of the verb.
Я вижу мужчину.
I see a man.
'мужчине' is the dative form of 'мужчина' and indicates the indirect object receiving the book.
Она подарила книгу мужчине.
She gave a book to the man.
'мужчина' is the nominative form and serves as the subject of the sentence.