"A girl is eating."
Both translate to "girl". "Dziewczynka" is rather a younger girl, while "dziewczyna" starts about the age of... 13, maybe? The border is not clear. "Dziewczyna" is also "a girlfriend".
No. "jem" is the form of 1st person singular, that is "I".
So for "I eat" you can either say "Ja jem" or just "Jem". But you cannot use it for any other person.
When you say dziewczyna also means Girlfriend, do you mean a girl who is a friend or someone's partner. Because this could lead to an awful situation if a 20 years old man of non native Polish happens to say his dziewczyna is 13 years old
OK, I've heard "girlfriend" being used for a friend by other girls, but I've never heard it used by a man, how could anyone interpret it differently than "partner" then? o.O
I wish this app taught sentence structure. Cause sometimes it tell you you are wrong and doesn't show you how sentences in the language are structured.
Telling somebody to eat something like pointing to the food and say "Yeah! "...