The Camera Component adds a camera to your entity. In Create, you can use it to define your 3D viewport.
If the camera is set to be the Main Camera, then the scene will get rendered through this camera when the scene starts. If you have multiple cameras, you can switch between these during both edit- and playback mode.
Follow Editor Camera
If this checkbox is checked, the camera will automatically set its position to the editor camera position. This is useful when switching between play and edit mode.
Projection: Perspective or Parallel
This setting controls how the camera will project the 3D world on the 2D canvas.
FOV: Field Of View
This value is the number of degrees from left to right that the camera will span.
Clipping planes: Near and Far
These numbers define where the clipping of the camera frustum will occur. Try to keep this range as small as possible to make sure to get good precision.
When an entity has a camera component, it gets a debug render of the camera and its frustum while in edit more: