Yeah, they're adding in this -un ending. It basically makes the noun indefinite, like "a garage" instead of "the garage" (which would be al-karaaj). The 'u' part of -un also shows the noun's case, which shows how the noun functions in the sentence, but it's not really relevant to know until we get longer sentences.
Why don't they tell us meanings of various words before asking sentences?
Very frustrating that they're asking me to answer words I've not been taught yet-- I obviously understand "karaj" is garage. But I couldn't know that "jadid meant new" nor that the adjective appears after the noun in Arabic. Is this always the case and is the word "a" implied?