A camera contains a list of viewpoints, and an optional list of keyframes to describe how the viewpoints move.
If no camera keyframes are defined, then the scene uses the current views in the Scene View. If a single keyframe is defined, the camera moves to that viewpoint, and then remain static throughout the scene. Finally, if multiple keyframes are defined, the camera is animated accordingly.
You can add a blank camera, and then manipulate the viewpoints, or you can copy an existing viewpoint animation straight into your camera.