The genius of this switch is that you can feed it yourself with POE++ and it can then supply up to 4 cameras with POE+! I use this switch with four UVC-G3-Flex-3 cameras and only need one Ethernet line with POE++ to feed everything.
Of course you can also use the switch with other cameras (without POE). But the Swich needs a POE power supply because it has no power input itself.

That was exactly my first question.
Second question. How long can the network cable(s) be to operate 4 Poe cameras?

Yes, it works without problems. The switch "notices" which end device is connected. But you can also deactivate it manually on the switch.