Configure modem to imac

Sorry?

What do you mean 'configure my modem to my iMac'?

Assuming you have a "modem" from your Internet service provider, I would imagine you just plug it in then plug your Mac into an Ethernet port on the device or join whatever WiFi network it is creating.... If you need more help than that, I suggest you contact your ISP or the modem manufacturer.

In all the years I have owned computers (well over 30 years) I have never seen a need to configure a modem to any computer.