rlaperu2
Read all the manuals again, linked at the top of this page.
In server only mode, one NIC is supported. If you have two NICs the only option is to bond them for a faster connection, other options are not supported.
The one NIC connects to your LAN switch or hub.
You should have another device acting as gateway & firewall & usually a DHCP server ie a router, which connects to the LAN on one side and the modem on the other.