It's called a wired/wireless router. If you have a router then perhaps it provides additional Ethernet ports. If it doesn't, the replace it with one that does Surely your cable provider can help you with the exchange.
You do not want to use a switch or hub if the modem does not have an Ethernet port separate from the one that connects to your computer. It would lack the security of a proper gateway/router.
The Apple Airport Extreme Base Station is a router that will work, but it cannot act as the cable modem. Ask your provider for a modem that can work the the AEBS as the network router.