This is the 50th most frequent Italian word.
primo
"Primo" means "first" in English.
In this sentence, 'primo' is used as an ordinal adjective to describe the earliest or foremost friend in one's life.
Mio cugino è il mio primo amico.
My cousin is my first friend.
'Primo' in this case functions as an adverbial element, expressing the sequence in performing actions or giving instructions.
Per primo, assicurati di leggere le istruzioni.
First, make sure to read the instructions.
Here, 'primo' is used as an adjective meaning 'first', referring to the order or sequence of the days in school.