Why instrumental? Does Polish not use the predicate nominative for subject complements?
In that link you posted there are some explanation of using Instrumental, this is the case here: [Instrumental is used ] with certain verbs "być" (to be), "zostać" (to become), "interesować się czymś/kimś" (to be interested in something): Basia jest dziewczyną - Basia is a girl. Adam jest chłopakiem - Adam is a boy. Piotr jest przystojnym chłopakiem. - Piotr is a handsome guy.
Just to remember - why Instrumental not Nominative, I would say it's like this "to be" would be actually mean "to be in a role of something".
Btw. I'm native Polish speaker, if you would have any questions - I will be happy to help. :)
i have no idea what instrumental case is or when it's there but i'm pretty sure i'll find out soon :^)
Actually it should be: Ja jestem kobietą (with ą - it's instrumental) or better: Jestem kobietą ( ommiting the pronoun is natural in Polish, while you can tell person in the sentence by the form of the verb).
This is only one word. "Jestem" is "być" - "to be" conjugated in first person singular in present tense. You usually don't use pronouns in Polish, except for clarification or emphasis - the same as in Spanish :).
i can imagine you have a very hard time explaining the word "być" to english speakers
So "Ja" is used when you want to use "I" or "me" on it's own. And "Jestem" is used when you want to say "am". But Jestem can also be used to say "I am" at the start of a sentence?
Verbs conjugate uniquely, unlike in English. You can tell from the verb what the pronoun would be, so you can easily leave off the pronoun.