The image sensor is the central component of a CCTV camera - the "eye" of the security camera, which detects the beam of light passing through the lens and converts it into an electronic signal.

The technical characteristics of the sensor are what determine both the resolution and the light sensitivity of the image given by the camera - the more pixels, the more detailed the image, the higher the light sensitivity, the better the image in low-light conditions.
The size of the image sensor together with the lens will determine the camera's angle of view.

All three of the above parameters are usually listed in the technical description of the camera: resolution in megapixels (Mpx); light sensitivity in lux (lux) and angle of view in degrees (°).

This is the basic information about image sensors, if you want to explore in more depth, more detailed technical info is available here.