This is the 8448th most frequent Polish word.
polakowi
"Polakowi" means "to a Pole" (dative case of "Polak").
In this sentence, "polakowi" is the indirect object in the dative case, referring to the recipient of the book.
Dałem polakowi książkę.
I gave the Pole a book.
Here, "polakowi" is used in the dative case to designate the person being helped.
Pomogłem polakowi z projektem.
I helped the Pole with the project.
In this instance, "polakowi" acts as the indirect object in the dative case, indicating the person receiving trust.