As you may have already found out by now, what you can and cannot do with that network switch "behind" the NVR is dependent on the NVR. Some systems have 2 (or more) Ethernet ports that create separate networks. In this case one of the ethernet ports is usually configured to connect the NVR to the outside world, and the other ethernet port/ports are a separate private network just for the cameras. Connecting to one of these secondary ports will not get you out to the internet.

Some NVRs may have multiple ethernet ports but internally the NVR acts like a simple network switch. The multiple ports are there for convenience, maybe supplying POE power to connected cameras. In this example connecting to any of the ports will get you connected to the main network (and presumably out to the internet) similar to connecting something to a simple 8 port switch.