Yeah NVR are short for Network Video Recorder, simple put it is just a network switch you can but a hdd inside to record the footage of the cameras on.
I have each of the 4 cameras wired to that box and then the box wired to a wifi router, this way i can see footage on my living room TV ( connected with HDMI to NVR ) and i can see footage on my computer as it is also connected to the router, and finally via the wifi in the router i can also see camera footage on my 7" laptop that's on my bedside table when i sleep.
NVR have motion detect and alarm and i am zoomed in on my car where it is parked, so if anything human sized come within 1 M of the car the alarm goes off and wake me up.
Some captures i have made.
Kitchen fire ( stove ) down on the first floor at the senile old lady that use to live there, this camera are replaced with IMX 185 camera now.
Demoing programmable tour on the PTZ camera, i would prefer a new model with track and zoom option.
This are the updated version of my NVR, now much better than the 4 year old model i have.
http://www1.dahuasecurity.com/products/nvr410441084116-4ks2-8211.html
There are some ways to do it, you can connect your cameras to a switch and then that to your computer, and so you can acess each camera like a web page, and if your computer are on all the time you can record on it.
Other cameras can offload their footage to a NAS ( Network Attached Storage ) box, and i assume being controlled via your computer also on same network.
This option let you turn off your computer as the cameras are offloading onto the hard drives in the NAS.
The NVR i have are i believe the more true CCTV solution, you can get them with as many channels as you like or can afford, my little one just support one harddrive up to 4Tb in size, the larger units support more hard drives and RAID configurations for data safety.
You control the cameras via the NVR using the standard languages like onvif and a range of other formats, but onvif seem to be the most used by now.
So i can turn and zoom my PTZ camera ( Pan Tilt Zoom ) using the software on my computer, the app on my tablet, or the wireless mouse i have connected to the NVR so i can control the mouse cursor on my TV screen.
ATM i dont have the computer connected to the system as i changed over to win 10 and have not bothered with setting up the software on the computer ( PC software came with the NVR )