It's instrumental, not accusative.

Nothing? It is a question word. It means it is a yes/no question. We often skip it in informal speach, but it is necessary in more formal situations or in writing. It is important to use when you can't rely on intonation to be heard.

"Czy" is that context would sort of be like the word "are" in "Are you...".

(Im polish ok xD) Czy mean are, or why

Or "or"

It is like the rest. It's in the instrumental case, dziewczynką. The "-em" ending is for gender-masculine nouns. "Dziewczynka" is a gender-feminine noun.

you must have made some mistake. Possible mistakes: 1) it's spelled "czy" 2) czy does not really mean "are", or "do", or any other word you put at the beginning of English question. It is a yes/no question word, you add it at the beginning of the sentence, but you still need the verb.

so "czy jesteś dziewczynką?" or "czy ty jesteś dziewczynką?"

Because that's asking, "Is it a girl?"

Do you mean pronunciation? Because there is no "jestesz."

Ś = /ɕ/

Sz = /ʂ/

The Ś is more palatalized than English "sh" /ʃ/, and the Polish "sz" is less palatalized than the English "sh." For the "sz" sound, the tongue is in the same position as English "r," but blows air like "sh"

Because you wouldn't speak to a child formally in Polish. A little girl is not Pani.

Because '-em' is a masculine/neuter ending, not a feminine one.

You have to learn noun cases in Polish. Dziewczynka is in the nominative case, and dziewczynką is in the instrumental case. After the verb "is/are," the noun takes the instrumental case in Polish.