First person pov uses an “I” narrator, meaning the narrator is the primary character. The main strength of this pov is that it gives absolute, unfettered insight into the character’s thoughts, feelings, and experiences. The reader becomes the character. This is the most intimate point of view. The main drawback of this pov is that the reader can only know what the character knows – you may have absolute knowledge of a single character, but you have no knowledge whatsoever about other characters, except what your primary characters thinks they are feeling/experiencing.
Note: limited knowledge can be a benefit, as it can help to keep secrets from characters and from readers.
When I teach first person pov in the classroom, I like to use a clip from Doom, a first person shooter, and ask students why first person is the best pov for this style of game. Answers range from the suspense it creates, to the immediacy and adrenaline rush you get while playing, to the way it forces you as a character to notice tiny details that might indicate an enemy nearby.
This relates directly to how it is used in fiction: while stories do not always have the suspense of monsters popping out from corners, good first person stories will always have some element of the unknown that keeps the reader wondering what will happen to the character next. Some stories give you an adrenaline rush, but good first person stories should always have a sense of immediacy so that the reader is fully invested in the character (this is true even if the story is told in past tense, or the character is relating something that happened long ago – think Frankenstein). And last, a good first person story will keep the reader engaged and looking out for clues as to what will happen next, because readers tend to want to be one step ahead of the character (people like solving puzzles).