This is the 4527th most frequent Polish word.
księgarni
"Bookstore" (genitive or locative form in Polish).
Here, 'księgarni' indicates the location where the action of buying occurs, reflected as the locative case of 'księgarnia'.
Kupuję książki w pobliskiej księgarni.
I buy books in the nearby bookstore.
In this sentence, 'księgarni' serves as the ablative case, referring to the source of assistance or connection.
Znalazłem interesującą książkę dzięki osobie z księgarni.
I found an interesting book thanks to a person from the bookstore.
Here, 'księgarni' denotes possession or association with the owner, in this instance reflecting the genitive case.