The 4 camera kit will usually consist of four security cameras and the recording unit along with the accessories that come with the kit. There might also be additional things in some kits such as the hard drive to store the video footage, power supplies, mounting accessories, and software or mobile app to watch the video footage remotely. Before buying, make sure to look at the camera resolution, camera field of view, night vision range, recording time and weather resistance of the cameras and recorder. Compatibility of the cameras and recorder should be checked too.