I see that you learn Brazilian Portuguese so remember that: Polish "ą" is similar to Brazilian "om" in "bom" and Polish "ę" is similar to Brazilian "en" in "quente".
OK, thanks, you are right, I edited my last answer giving some better example ("en" in "quente").
Desculpe. Você tem razão. Isso foi um erro. Aquela resposta é muito velha, então agora não lembro porque dei este exemplo. Provavelmente pensei sobre "sentou", mas esta palavra não tem este sonido nasal. Talvez o melhor exemplo é "quente", então "reparei" a minha resposta. Obrigado pela tua vigilância. :)
"Ona je žena." But actually, I read a comment in a different discussion that explained Polish cases in more detail and said that instrumental (with the questions "kim?" & "czym?") can be used to express who you are - as in "Who am I?". And I realized that you could actually say that in Slovak using instrumental too ("Ona je ženou."), and it is absolutely correct, it's just not at all common because we would only use it as an answer to a specific question - which is probably the reason it didn't come to my mind immediately. Funny :)
Yes, all "Y-nouns" in sentences like: "X-noun is Y-noun" or "X-personal pronoun is Y-noun" take this case.
Yes, you are right. As I wrote - it only works with nouns and personal pronouns, while "Y-nouns" in sentences like "X-demonstrative is Y-noun" take the nominative case, so "Ja jestem kobietą", but "To jest kobieta".
Feminine, singular nouns (they mostly end with "-a") get this ending in Instrumental Case. Just change "a" for "ą" and that's it ;)
Thanks. I've also noticed that it's the same with masculine nouns. Is that correct?
Exactly. For every singular noun ending with "-a" this is the rule. I cannot recall any exception for this.
In Polish every grammatical person has their own form of a verb. "jestem" is for 1st person singular. "jest" is for 3rd person singular.
Right now you know "kobieta" (Nominative = the basic, dictionary form. Mostly used as the subject of the sentence) and "kobietą" (Instrumental). Sentences like "I am Y" or "She is Y" take Instrumental (if Y is a noun phrase). I guess you might have seen "kobietę" as well, that's Accusative. Generally Accusative is used for the direct object of the sentence. Almost all verbs encountered in the beginning of this course take Accusative.
I can feel your pain. It is hard at the beginning.
"she is a woman" ---> "ona jest kobietą"
"I am a woman" ---> "ja jestem kobietą" or "jestem kobietą" (in Polish you can omit "ja" unless you REALLY want to put emphasis on you being a woman, like "I am a woman (and the others are just girls)"
"this is a woman" ---> "to jest kobieta" (there is no "ą" at the end)
I'd advise you to look up online all the cases of Polish nouns and how to use them. Spend a day or two studying them hard and this will be a HUGE help for you going forward.