The system you bought is wireless equipment.
Wireless means the camera can connect NVR wirelessly, but it doesn't mean NVR can connect router wirelessly. Please don't misunderstand it.
1. Why is there a cable in the package?
The ethernet cable in the package is used to connect NVR to the router to get the Internet, not used to plug the camera to NVR.
2. Why is there an ethernet port at the end of the camera and 4 ethernet ports at the back of NVR?