This is the 222nd most frequent Croatian word.
prva
"Prva" means "first" (feminine form) in English.
Here, 'prva' is used as an ordinal number to indicate the position of a person in a sequence, specifically being the first.
Prva osoba u redu je čekala satima.
The first person in line had been waiting for hours.
In this sentence, 'prva' is used as an ordinal adjective describing the noun 'knjiga', showing its sequence as the first read by the subject.
To je bila prva knjiga koju sam pročitao.
That was the first book I read.
Here, 'prva' acts as an ordinal descriptor for 'stvar', denoting the sequence of noticing events described by the subject.