I use a router. It can allow for 4 computers to be networked. The internet cable plugs from the wall to the router, and the cables from your computers connects to the router.
Basic Networking.
If you are just wanting to hook them up together you can simply use a crossover cable to connect them up directly to the Ethernet ports.
But if you want to allow them both to...
1. Go buy a piece of equipment called a "hub" or "switch" and some "ethernet cables" 2. Hook the computers to the hub with the cables. 3. Next you'll have to figure out how to assign your IP...
Press Win+R, then type cmd. In cmd window type netstat. It will show you all connected computers to the one you are using at the moment. You can use different parameters to sort netstat output.