I will be detailing on how to set up / replace a modem to create a wifi network.
You'll need :
Modem and power cord
(Possibly a router)
Ethernet cables
Coaxial cables

Step 1: Plugging in the Cords

Connect the coaxial cable to the wall outlet where the Internet comes from. (Satellite, phone line, etc) then connect it to the modem itself. While you're at it, plug it into the wall. Turn it on if it has a switch.

Step 2: Plugging It in to the Router

Then you'll need to plug an Ethernet cord into the modem, and the WAN port on the router. Plug in the router to an available power source. Next hook an Ethernet cord from the router into your PC. After its all hooked up, you should have Internet. You may need to do additional steps on your computer to fine tune your network.