The narrator is thus directly or indirectly involved in the story being told. A strength of first person narrative is that the character may also express feelings, thoughts, and experiences, and may reveal him or herself; therefore, the reader usually gains keen insight into the life of the narrator. First person POV can also be used to withhold information from the reader, particularly information not available to the narrator.
The intensity of such confessional intimacy can be striking. First person narratives can appear in several forms: interior monologue, as in Dostoevski's Notes From Underground; dramatic monologue, as in Albert Camus' The Fall; or explicitly, as in Mark Twain's The Adventures of Huckleberry Finn.
Since the narrator is within the story, he or she may not have knowledge of all the events. For this reason, first-person narrative is often used for detective fiction, so that the reader and narrator uncover the case together. Agatha Christie's The Murder of Roger Ackroyd turned this principle on its head by revealing at the end that the narrator had been the killer all along, and had been withholding information from the reader.
First person plural narrators tell the story using "we," that is, no individual speaker is identified; the narrator is a member of a group that acts as a unit. First person plural POV occurs rarely but can be used effectively, sometimes as a means to increase the concentration on the character or characters the story is about. Examples: William Faulkner in "A Rose for Emily" (Faulkner was an avid experimenter in using unusual points of view--POVs--see his "Spotted Horses," told in third person plural), and more recently, Jeffrey Eugenides, in his novel "The Virgin Suicides."
First person narrators can also be multiple, as in Akutagawa's "In a Grove" (the source for the movie "Rashomon") and Faulkner's novel "The Sound and the Fury." Each of these sources provides different accounts of the same event.
The first person narrator may be the principal character or one who closely observes the principal character (see Emily Bronte's "Wuthering Heights" or F. Scott Fitzgerald's "The Great Gatsby," each narrated by a minor character).
First-person narrative can tend towards a stream of consciousness, as in Marcel Proust's A la recherche du temps perdu. The whole of the narrative can itself be presented as a false document, such as a diary, in which the narrator makes explicit reference to the fact that he/she is writing or telling a story.
Perhaps the most convoluted example of a mixed media kind of POV is Joseph Conrad's novelette "The Heart of Darkness," which has a double framework: an unidentified narrator describes (in first person plural) Marlowe, the principal character, telling his own story in the first person. Thus we have a "we" describing a "he" who talks about "I."