I wrote "Those sentences are good" and I believe that it is a better translation than just "sentences are good". Is there a reason why it wouldn't that be the case?
In the Czech sentence, there is no demonstrative (e.g., Ty/Tyto/Tyhle) to indicate that we're talking about some particular sentences. Without it, we're talking about "sentences" in general. (However odd that might seem...)
Nope, that would work in Russian (which you perhaps compare with?) but not in Czech.
do you mean that in russian it would be a general word "sentences" at all, and in czech it is a particular sentence?
The other way round.
In Czech it is a general statement about sentences in general.
In Russian it could be about particular sentences (the sentences are good). But I see I shouldn't have mentioned Russian at all, it will just confuse you.
Forgetting about russian, I think I understand. Jablka jsou dobra' means apples at all and Ty jablka means Those apples.
This "sentence" is a grammatical structure that contains a subject and a verb -- or, as you said, "sentences that form paragraphs."