it is difficult to explain by Armenian grammar, I'll try to explain on examples.
հագուստ = clothing
when we want to say "part of the clothing" we say "հագուստի մաս" that is we mentioned the affiliation
or
փողոց-street
on the corner of the street-փողոցի անկյունում
or
Lilit-Լիլիթ
Lilit's bag-Լիլիթի պայուսակը, that is the bag belongs to Lilit
if there are any questions, feel free to ask...