nominative: rajulun a man(subject) ar-rajulu the man(subject) rajulu the man of….(subject)
genitive: rajulin (of) a man ar-rajuli (of) the man rajuli (of) the man of…
accusative: rajulan a man(object) ar-rajula the man(object) rajula the man of…(object)
the genitive is not just used in possession, but also after all prepositions.