Yes and No. The names of the genders are masculine, feminine and neuter but it doesn't mean that masculine is only for men/boy and feminine is only for women/ girls or neuter only for things. It's just a way of putting words into groups. So, don't be surprised when you see: ''το κορίτση'' (the girl neuter) ''η καρεκλα'' the chair feminine. And ΤΟ is for neuter)
Why greek language uses η,υ,ι,ει, to express the sound i
Because of sound changes. A bit like how in English, "meet" and "meat" now sound the same, even though "ee" and "ea" used to stand for different pronunciations.
why to make the sound psi they invent a letter not just write πσι,
Ancient history. Some Greeks did indeed write πσι, while others wrote ψι -- the alphabet that "survived" was from an area that used ψ for the πσ combination.
Similarly, some Greeks used Χ χ for the /ks/ sound rather than for /kh/ -- which is why "X" has the sound value it does when the Romans based their alphabet on the Greek one.
Option 1 - learn the gender together with the noun
Option 2 - look at the ending of the noun.
Masculine endings include -ος -ας -ης -ες
Feminine endings include -η -α -ος
Neuter endings include -ο -ι -μα -ος
άντρας has -ας and is masculine; γυναίκα has -α and is feminine; κορίτσι has -ι and is neuter.
(Nouns in -ος can be any of the three genders, but are most often masculine.)
Nouns in -α you have to see whether it's -μα: then it's almost always neuter, otherwise (almost always) feminine.
There are also other endings (e.g. η μαϊμού), and some of those endings can belong to another gender (e.g. το κρέας, το γάλα), but the ones above are the most common ones.
Actually, in most cases, the sequences ντ and νδ are interchangeable.
When I was taught Ancient Greek at school I learned the definite articles in the Nominative as: ὅ, ἥ, and το. Has the rough breathing (h-sound) disappeared completely from these in Modern Greek, or is it still there in regional dialects? And has the accent gone too from these words?
"By the 4th century AD, the loss of vowel length distinction and aspiration was most probably generalized." ( https://en.wikipedia.org/wiki/Koine_Greek_phonology#4th_century_AD )
Aspiration continued to be written for centuries out of tradition, but I would be highly surprised if it survived even in some out-of-the-way rural area. I've never heard of aspiration surviving in Modern Greek.
As for the accents, the monotonic system that Jaye mentioned stopped writing the breathings (that had long since been lost in pronunciation anyway) as well as replacing the three different accents (which had been pronounced identically for centuries anyway) by just one and placing it, in writing, only on polysyllables.
There are only a handful of single-syllable words that have an accent, to distinguish them from homographs without the accent, e.g. ή "or" to distinguish it from η "the".
Incidentally, to the best of my knowledge, ὁ and ἡ were written without an accent in Ancient Greek as well when they were used as definite articles.
"Following the official adoption of the Demotic form of the language, the monotonic orthography was imposed by law in 1982. The latter uses only the acute accent.. and diaeresis and omits the breathing." https://en.wikipedia.org/wiki/Greek_diacritics#Accents
IT asks me to select missing word, There are no words to select from! The only thing I can do is skip and then it just keeps coming up with the same page! Very frustrating as I can't progress. Have reported it but have had no reply. Have noticed other people mention this but can see no solution. HELP
It's really hard to reply without more information. Is this an exercise where you have to choose the right word?
Is the ο covered. Try making the script smaller. Or choose the option to use the keyboard which should be possible. But again since we can not see any of your work you should send a screenshot.
I am a little confused by your request.
Would this help you ?
If these do not assist, can you try to explain the problem again. It is that you are unable to type in Greek ?
Why doesn't it accept the variant “Ο άνδρας”? https://en.wiktionary.org/wiki/%CE%AC%CE%BD%CE%B4%CF%81%CE%B1%CF%82
Yes, I can understand that. And that's why we went to a lot of trouble to prepare links to show you not only how to access the Greek keyboard on your computer/phone etc. But also to provide hints on how best to learn on Duolingo etc.
So, just read the comments below yours for all that information and more.