This confused me too, but according to this page (http://www.foundalis.com/lan/grkalpha.htm) it's because they were two different sounds in ancient Greek that have ended up sounding the same in the modern language! Omicron was a short "o" as in "got" and omega was a long o like the "aw" in "law. Nowadays both are "o" as in "got".
The three "i" sounds (ι η υ) have a similar background :)
I think it would better to use IPA than letters of an English word, which can be pronounced many different ways.
Omicron (Ο/ο) was and is /o/. Omega (Ω/ω) went from /ɔː/ to /o/.
Iota (Ι/ι) was and is /i/. Ēta (Η/η) went from /ɛː/ to /i/. Ypsilon (Υ/υ) went from /y/ to /i/.
And then there's the consonants and diphthongs. Hope that helps.
You will need to learn every word with its spelling, there are some rules but they are not enough to explain why words are spelled the way they are. Something you will see for example in the next lessons is that active voice verbs in the first person always end in -ω, like κάνω-to do, θέλω-to want. No exceptions.
More info about this case, as I asked to a Greek friend:
[26/7 11:39] Pavlos Nikolau: But ξυλόφωνο the second word is φωνή which means voice and its written with ω [26/7 11:39] Pavlos Nikolau: The second o is because of the nature of the word. τΟ ξυλόφωνΟ [26/7 11:40] Pavlos Nikolau: This is not male or female and the words whose have no sex in greek language are written with omicron in the end.
So if its neuter (το ...) in the end it will have omicron.
To activate the Greek keyboard in your device, see the information posted at MODERN GREEK RESOURCES How to get the keyboard and much more.
The team has posted a lot more on resources in the Greek forums at https://forum.duolingo.com/topic/936 .
“fetting parr?” = “getting part?”
Here on the user discussion forum there's little to no chance that a Duolingo responsible will read your proposal. We are all learners like you. You could try posting on the support forum.
Remember that Duolingo is not a Dungeons and Dragons game where your objective is to get to the next level. Here (I think) your objective is to learn Greek. A wrong answer means that Duolingo will present you with the same exercise again, and that's useful. If it accepted partly correct answers you would never learn the really correct answers.