"Are you a man?"
Translation:Czy jesteś mężczyzną?
"Człowiekiem" would mean man as in a member of the human race. So "Jesteś człowiekiem?" might be like in a fairy tale or a myth with centaurs, mermaids, or talking animals. A creature meeting a human for the first time might ask "Are you a man?", even if they are talking to a woman, a boy, or a girl.
"Jesteś mężczyzną?" should work.
Czy doesn't mean are/is. It has several meanings, but here it's just a question marker, like "is it true that...", or "I would like to know whether..."
About the difference between "to" and "być" you can learn here: