but in italian "What are you eating?" will be "Che cosa stai mangiando?" It is correct?
Yes, it is correct. (In English, when asking, the verb goes first. You must say: "Is it correct?".)
I agree. Can that be used, instead? I didn't want to lose a heart, so, I didn't try it.
How do you know it is present tense ("What are you eating?") rather than past tense ("What did you eat?")?
Past tense has a different construction. This form of the verb mangiare, "mangi", is only used in the present second-person singular (as well as a few forms of the subjunctive, which Duolingo doesn't touch upon until WAY later, so don't worry about that right now); in other words, "mangi" only (at this point in the lessons) means "you (singular) eat (present)."
The past tense, "What did you eat?" would look something like "Che cosa hai mangiato?"
Instead of "What're you eating" I almost put " What;re thooooossssseeee!?!?!?"
why 'cosa' and not cos'e´? What is the difference in the two? Is cosa for a "thing" and cos'é for a person?
It's not about the gender. It's easy: "Cosa" means "what". "Cosa é" means "what is". In other situations you can translate "cosa" with "thing". Example: "Racism is a stupid thing." ➡ "Il razzismo é una cosa stupida".
My Italian friend always says "Cosa?" to his parents after they say something to him.
How would you know the question "what"? I see the definitions for "you eat" and " thing."
Thanks. I finally figured that out. But you wouldn't know from reading the definitions offered.
I think Italians may also use "che cosa mangi?", which is a bit easier to figure out.