"They are women."
I'd say it depends on the context. If you are talking about them for a while you won't say, "Yes, but those are women, they should be aware of blah blah blah". "they are women" sounds much better here, and I think it's the same little nuance in Russian. Tell me if I'm wrong 'cause I'm French x)
Not sure but i think это is for THIS IS and они is more like THESE ARE like ... они is more like "them" and это more like this is. "This formation of people are called women" "these specific people in your list are all women" kinda way. It's hard to explain, and I may be wrong, but i think that's the difference.
In this case, it's because it's plural Women, whilst женщина would be singular woman. Judging from your levels, I'm assuming that you're starting in English?
Russian uses different suffixes instead of prepositions for plural and different relationships between nouns and verbs. I found it useful to look up the technical terms and definitions for some of the cases in English, Grammatical Cases on Wikipedia was quite a good starting point. All the suffixes in Russian follow rules in how they're constructed, unlike English where there's sometimes more exceptions to the rule. Just gotta learn and practice the rules and you'll get the hang of it ^^
If you can't find it, this is not a Russian keyboard propably. Remember, many languages use Cyrillic alphabet, maybe you are using a Ukrainian keyboard, and Ukrainian does not have this letter. Take a look and see the name of the language written on the keyboard space bar, if it is written "Русский", then there must be some error, which I believe it is not.
Dear Duolingo, stop letting me pass when i type "Она" instead of "Они" unless these are the same words. If I have a typo DO NOT pass me. It hurts my ability to remember the correct spelling and usage the first time. Sometimes, I don't realize that I have a typo until I am tapping to the next screen and I don't know what my mistake was.