This is the 184th most frequent Croatian word.
prve
"Prve" means "first" in English, as the feminine plural form.
Here, 'prvih' is the feminine plural genitive form of 'prvi', used to describe 'knjiga', indicating 'one of the first'.
Ovo je jedna od prvih knjiga koje sam ikad pročitao.
This is one of the first books I ever read.
Here, 'Prve' is the feminine plural nominative form of 'prvi', referring to 'ptice', to denote 'the first'.
Prve ptice ujutro pjevaju najglasnije.
The first birds in the morning sing the loudest.
In this sentence, 'prve' is the feminine plural nominative form of 'prvi', matching 'cipele' to signify 'the first' owned by the speaker.