The genitive case(حالة الجر)  is the case of nouns that occur after prepositions or as second word in idafa constructions, and their modifying adjectives. Nouns and adjectives that are genitive are called (المجرور) in Arabic.  There are various endings used to mark the genitive case; depending on the number, gender and definiteness of the noun or adjective in question.

Definite singular (and broken plural) nouns and adjectives are marked by (كسرة) which is written as (ـِ), and sounds like a short /i/

تكلمتُ مع الطالبِ الجديدِ.

“I talked to the new student.”

كتاب الطالبِ جديد.

“The book of thestudent is new.”

Indefinite singular (and broken plural) nouns and adjectives are marked by (تنوين الكسر) which is written as (ـٍ) and has the sound /in/

تكلمتُ مع طالبٍ جديدٍ.

“I talked to a new student.”

Dual nouns and adjectives are marked by the suffix (ين)

تكلمتُ مع طالبين جديدين.

“I talked to new students (masculine dual).”

Sound masculine plural nouns and adjectives are marked by the suffix (ين)

تكلمتُ مع المدرسين اللبنانيين.

“I talked to the Lebanese teachers.”