Third person is a narrative perspective that does not assume a particular character identity and refers to characters using third-person pronouns such as he, she, they, him and her. Writers use this when they want to tell a story from a distance or give an objective account of information.
Third-person point of view is sometimes omniscient, an all-knowing narrator that sees every action and all characters' thoughts. In other cases it is more limited, and the narrator only knows about the behavior of a certain character or group of characters.
First-person point of view, in contrast, is written from a main character's perspective and uses personal pronouns. This voice is used in narrative when writers wish to focus on the thoughts and feelings of one character.