The idāfa

Two nouns side by side mean of: باب البيت (the door of the house), كتاب الطالب (the student's book). The first noun never takes the article or tanween.

The whole phrase is definite when the last noun is: مدير المدرسة (the school's head). A feminine first noun keeps ة but reads it as t: مدينة باريس.

An adjective comes after the whole construction: باب البيت الكبير can mean the big house's door; context decides.