When are you going to consistently focus on teaching the full conjugation of one verb at a time. It is very frustrating flitting about like a fly.
it says "Ty máš dobré kafe." in my answer, but i thought kavu/kava was the word and not kafe?
"Kafe" is colloquial and very common in normal speech, "káva" is standard Czech. Duolingo guesses the closest accepted sentence to your attempt, so if you used "dobré" it might have found "kafe". "Kafe" is neuter and "káva" is feminine.
why in here use "dobrou"?
can this sentence also be sg. ?
so can use "Ty mas dobra kava"
See the Tips and notes about grammatical cases and the accusative case in particular.