How can i write in the greek alphabet here? I wrote it with latin and it wasn't correct?
The Greeklish (Greek with Latin characters is not accepted by Duolingo yet). You should change your keyboard into Greek in order to play the course.
I hope you don't accept Latin characters in the future, it is a real trap and would eventually slow up your progress making it more difficult to read Greek texts. I know it's very popular in text messages for "cool" young Greeks but they already have learnt to read in Greek characters.