Someone forgot to add the " ٌ " diacritic to the end of the word "garage"/"كراج"; with the way it's pronounced right now, it should be written like this "كراجٌ". The " ٌ " adds an "-un" sound to the end of a word. Now I'll just let someone more expert than me explain when this diacritic should be used. But know that it's not that strict, and in everyday use it can be dropped.
Yes, an adjective always come after the noun it modifies.
The -un you hear is the case ending of an indefinite noun in the nominative case.
Nouns and their adjectives always share the same case. So even though Duolingo does not enunciate the case ending for the adjective, Arabic grammar still says it's there. (In spoken colloquial Arabic, case endings are rarely enunciated for either the noun or the adjective.)
Not only do nouns and their adjectives share the same case, but they share definiteness. That is, if the noun's indefinite, then so is the adjective that modifies it. If the noun's definite, then so is its adjective.
A definite noun and its adjective (when in the nominative) would take an "al" prefix and an "-u" case ending. So, like this:
karaajun kabiirun = A big garage
al-karaaju al-kabiiru = The big garage
kitaabun kabiirun = A big book
al-kitaabu al-kabiiru = The big book
Again, keep in mind that Duolingo does not appear to enunciate the case ending on the adjective. And as noted above, case endings are rarely enunciated in spoken colloquial Arabic. But they are used in MSA and fusha.
Also, when the noun/adjective is in the genetive or accusative case, they will take different case endings ("i" and "a""). But you'll learn that in due time.
how are we supposed to know these words? i haven’t learned anything but sounds except for Peru Dakar, etc. these you can sound out because they sound like english words. we haven’t learned what big is in arabic. i’ve never done anything like this before. i’m ready to give up.
"The house" would have the Arabic word for "the" attached to it. As you probably already know, there is no word for "a" used in the present tense in Arabic. The word for "the" in Arabic is "al".
The "-un" attached to nouns and adjectives shows that the words are in the nominative/subjective case. In other words, that the word is the subject of the sentence.
Native speakers on the threads are also saying that if "-un" is attached to a word it also means "a". I just look at "-un" as showing the nominative case, though, because if there is no "al" attached to a noun, like "albeit", it has to be "a house" instead of "the house" whether "-un" is attached to the word or not.
We haven't gotten to this in the lessons yet, but I have a question about nunation (-un) and the definite article "the". I suspect that "-un" is used with nouns that have definite articles, also. But, no one has talked about that yet.
Nunation, btw, is used in Classical Arabic and MSA but not in Arabic dialects.