"The girls read a newspaper."
Translation:Τα κορίτσια διαβάζουν μία εφημερίδα.
You can put it wherever you want. Τα κορίτσια διαβάζουν μιαν εφημερίδα, μιαν εφημερίδα τα κορίτσια διαβάζουν, τα κορίτσια μιαν εφημερίδα διαβάζουν etc are valid but change where emphasis is put. In this course we follow the SVO order because it is impossible to add all possible orders for all possible sentences. Greek's syntax is very flexible.
See here for how to access the many links we have to help learners. https://forum.duolingo.com/topic/936
In particular you should start here:
TIPS TO HELP YOU LEARN + HOW TO REPORT A PROBLEM
To add the accent. When you are on the Greek keyboard, you first click on the letter on the right of the L [:/;] then the letter you want the accent on.
Why use ta and not oi?
Because κορίτσι is grammatically neuter, not masculine or feminine.
The grammatical gender is not necessarily connected to anything in real life.
το αγόρι (the boy) is also neuter, though boys are male. το άτομο (the person) is also neuter, though a person can be male or female.