"The new house resembled the old one."
Translation:Det nya huset liknade det gamla.
It is "ett nytt hus", but for the definite form it becomes "det nya huset":
en ny bil - den nya bilen
ett nytt hus - det nya huset
flera nya cyklar - de nya cyklarna
You have to put the adjective in the definite form as well, which is nya.
I still don't understand when you use definite form or what that even means.
The definitive form means there's a reference to a specific thing, not any one of a thing. For example, "the house" is definitive while "a house" is not.
In English, adjectives and nouns don't change when they are definitive, but in Swedish they do. So it's "the new house" and "a new house" in English, but "det nya huset" and "ett nytt hus" in Swedish.