"A woman is eating."

Translation: Kobieta je.

[Nadia548647]

Why is it sometimes kobietą and not kobieta?

[JerryMcCarthy99]

You probably know the answer by now (you are at level 11 as I write this), but "kobieta" becomes "kobietą" in a sentence such as "I am a woman" -> "Jestem kobietą".

[ghada33806]

can any one explain why we should not use jem although it means eating ???

[tadjanow]

"jem" = "I eat"/"I'm eating"

Here you need a 3rd person singular form, which is "je".

[DimaG22]

What's the difference between "je" and "jem"?

[JerryMcCarthy99]

"Je" -> "He/she/it eats". "Jem" -> "eat".

For more details than you possibly want at this stage, take a look at https://en.wiktionary.org/wiki/je%C5%9B%C4%87 and click on the "Conjugation" tab.