"A woman is eating an apple."
Translation:Kobieta je jabłko.
These are different cases, therefore they are different 'versions' of the word. We usually rather call them separate letters, then letters with diacritics - especially ą and ę. Just the fact that ą is more or less the 'ou' sound makes it totally different. In your sentences, the first one is in Instrumental and the second is Nominative.
Polish nouns have "declension," meaning they change form based on their grammatical role. "Jabłko" is the correct singular form for the nominative, accusative, and vocative case (sentence subject, direct object, and person being addressed). "Jabłka" is the plural of those cases as well as the singular of the genetive case (roughly, "the apple's" or "of the apple").
(No, I can't think of a situation where you'd use "jabłko" in the vocative case.)
Back to the beginning of this course :), now i know a bit more about this extreme hard language (++++cases) but my question here is: -the verb jeść is follow be accusative (or genitive if a negation) jabłko is neuter (nijaki) so in accusative stays the same way as the nominative case right, but that doesn't happen when it is a żeński (feminine) word, could anyone help here a bit just about the declesion differences between męski, nijaki and żeński, i live in poland and i struggle with this question everyday :l, thanks in advance to Jellei he has been my polish hero for about 2 years now :)