Using a router, you can connect the router through its WAN-port to the internet, using the ISPs IP and DNS-addresses. The other PCs connect to the LAN-ports of the the router, setting up either automatically using DHCP from the router, or by assigning individual IPs per PC in the 192.168.0.x where x = 1 - 255.
Make sure you get a router with a SWITCH and not a HUB.
Also check that you can "piggyback" more extra switches to the router for participation of more than the 4 or 5 ports a router normally has.
Hubs let through only one traffic at the time, whereas switches let all traffic through simultaneously.