Just as cameras are used in films to display the story to the audience, Cameras in Unity are used to display the game world to the player. You will always have at least one camera in a scene, but you can have more than one. Multiple cameras can give you a two-player splitscreen or create advanced custom effects. You can animate cameras, or control them with physics. Practically anything you can imagine is possible with cameras, and you can use typical or unique cameras to fit your game’s style.
For further information, see the Camera Component reference page.