GS605 outputs only one IP

[Gapter]

I connect the GS605 to my modem (does it matter which port?)

If I connect only one cable (say Google wifi), it works fine

When I add a second cable (say for smart tv or vonage), then the second cable is not receiving an IP address

All cables thoroughly tested.

Extremely frustrating,

[plemans]

the GS605 is a unmanaged switch. It doesn't have any dhcp/nat capabilities. 

You need to go modem--->router---->switch--->devices

[Gapter]

Indeed that is what I have (not sure what would be a router in this context). 

From what I see routers, have multiple internet outputs, if I use a router, why should I need the GS605?

Motorola modem (one output) -> Switch (netgear) -> devices

[plemans]

The vast majority of ISP's only assign 1 public ip address. A modem only device supplies that public ip address to your router. Your router is what takes that and assigns private ip addresses to the devices on your network. A modem only device can't do that. Neither can a simple unmanaged switch. (there are fancier switches that can but they're more expensive than a router)

You need a router that assigns those private ip addresses to your devices.