It depends on how the cameras are connected.
The easy way is finding out the model, looking it up on the internet, get the software, connect to the network and start the software it may show up the cams. But that will only work with poorly configured/secured cameras. (this have a very low rate of success though)
I guess you should start by scanning the network since most probably the data from cams is not available on the network itself but travels internally to the storage where there might be an interface to connect and see the feed or wired to a screen in which case it's more complicated to get access to.
Anws make some recon and try to be more specific.
Depends on what network you think you are scanning.
If there is an IT party that takes itself even the slightest bit serious this is not directly availible from whatever network you connect from.
It would be on a different VLAN, would be IP filtered and have proper auth/encryption.
There is no real advice except for learning the network.
Take notice of DHCP servers , DNS, ranges etc.
You can bet your ass that any camera system is routed, through NAT or completely seperate.
I could go on but this thread is probably gonna end up burried.