Learn Polish: Ona jest tam.

Yes, you can! Polish often drops the subject pronoun (like ona, on, or ja) if it is already clear who you are talking about. However, using ona here clarifies exactly who you mean or emphasizes that she is the one over there.

How do we know to use jest here?

Jest is the he/she/it form of the verb być (to be). Because the subject is ona (she), we must use jest. If the sentence was about yourself, you would use ja jestem (I am), and for the person you are talking to, you would use ty jesteś (you are).

Is ona only used for female people, or can it be used for objects too?

Ona translates to she, but in Polish, every noun has a grammatical gender. Therefore, ona is used for female people, but also for any grammatically feminine object, like kawa (coffee). If you are looking for your coffee, you could say Ona jest tam to mean It is there.

Could I change the word order and say Tam jest ona?

Yes, Polish word order is very flexible. Tam jest ona is grammatically correct, but changing the order shifts the focus. Ona jest tam simply states where she is, while Tam jest ona places a stronger emphasis on the person, similar to saying Over there, that is her.