"Is it coffee or borsch?"
Translation:Это кофе или борщ?
это - this is (introduces a subject)
этот - this (modifies a noun)
Это is a pronoun, while этот is an adjective; этот most also inflect for gender and number.
This is a woman.
this leg / this foot (f)
this chair (m)
this tree (n)
these ears (pl)
I hope that that wasn't too confusing. For now, just know это as a pronoun, like "this is", and этот/а/о/и as an adjective, like "this thing".
You're right in general, but it doesn't apply to this case. A lot of things in Russian are about how they sound and it just sounds wrong to a native speaker such as me. If you say "он кофе или борщ", in this case, it would sound as though you're 1) talking about a human which would make no sense, or 2) just saying something weird in general. So I recommend using "is this coffee or borsch?" in English and "это кофе или борщ" in Russian.
I don't think that 'а' corresponds to 'or' exactly - 'а' is like a cross between 'but' and 'and'. Maybe there is a particular instance where 'а' is more like 'or' - but I don't think it's this one.
Like you can say: это не кофе а борщ - That is not coffee, but borsch
But your version with 'а' above would be: 'Is it coffee but borsch?' - which as you can see from the English, doesn't work.
HOWEVER, I am not a native speaker and looking at our levels, my Russian is not better than yours - so I don't know that for sure you can't use a here - and we'll have to await further confirmation :)