This is a word of masculine grammatical gender, therefore the correct article is ο. The word itself ends in -ας, nothing you can do about it! Feminine word examples: η γυναίκα (the woman), η πόρτα (the door). Neuter word examples: το παιδί (the child), το κορίτσι (the girl), το αγόρι (the boy), το τραπέζι (the table). Be patient, the more lessons you see the more gendered articles (and word endings hopefully) will start making sense. Happy learning!
I have try to write the word but i don't find the first ''a ''on the greek keyboard. Thank you for your help.
If you have a physical keyboard, try pressing the key next to the L (semicolon on a US keyboard), then A -- that combination should give you an accented ά.
If you have an on-screen keyboard on a mobile device, try long-pressing the A key.
Άνδρας is the ancient spelling. δ in ancient times (until around 2-1BC) was pronounced as "d". Generally, all words with "δ" swifted their pronounciation to what we have today for δ, but some everyday words didn't. Those words (such as άνδρας) had their spelling changed to express the old pronounciation (with d) and άνδρας became άντρας. But the ancient spelling is still around so you can say either. In verbal speech it's one hundred times more possible to hear άντρας than άνδρας, though.
Duolingo uses uppercase Ο, for uppercase T(he). That's a kind of help we should not have. Anybody should see that "η" is wrong because it's lowercase. Same "problem" is found in a lot of alternative answers.