if the noun a pronoun represents hasn't been introduced into the context of the text or conversation yet, you always use the singular neuter form of the pronoun.
- det er ei god bok: it/that is a good book.
- dette er bøkene jeg leser akkurat nå. these are the books i'm reading right now.
- det er vakre sko. those/they are beautiful shoes.
but if using the words as determiners (coming right before the noun itself) then you'll match gender/count.
- den boka er god. that book is good.
- jeg leser disse bøkene akkurat nå. i'm reading these books right now.
- de skoene er vakre. those shoes are beautiful.
and you'll also match gender/count if the noun has already been introduced.
- jeg så en film i dag. jeg liker den. i saw a film today. i like it.
it's one of the more difficult things for native english speakers to learn since we always match count.