First person narrative is told from the point of view of a character within the story ("I called out to him as he left"), while the little-used second person narration uses the imperative form, directly addressing the reader ("You need to look out your window").
Third person narrative doesn't stem from a role in the story. The narrator is detached and separated from the action.
Third person narration uses the "he/she" form of writing (for example, "He drew his gun and aimed it at the police").
Third person narration is often omniscient, which means it can travel to multiple scenes and locations, and observe actions which no single character can.
Third person narration benefits from being able to convey information quickly and easily, unlike other forms which require more storytelling finesse.