u/505Griffon

I just purchased and did a basic set up of the wired RLK8-510B4-A which has 4 cameras. The current location of the DVR will make running an Ethernet cable quite difficult but not impossible to my fiber modem. Is there a simple and cheap wireless device I can add to the DVR so I don't have to run the cable? Please explain like I'm a 6 year old as not sure if should be a switch or modem. Simplicity is ideal.