as a determiner (followed by a plural noun): Several buildings were damaged by the explosion.
as a pronoun: If you want to see Edward’s paintings, there are several in the city art gallery. (followed by ‘of’): ♦ I’ve introduced her to several of my friends. ♦ Several of us will be attending the conference.
as an adjective (after a word such as ‘the’, ‘his’, or ‘these’, and followed by a noun): Ariel is one of his several nieces. ♦ These past several weeks have been difficult for the whole family.