A Network Interface Card. These are refered to as NIC cards. You can get one at any store that has computer supplies. It runs around $10-20 depending on who makes it. You need enough CAT 5 cable with RJ45 connectors to hok into the NIC and router. Use the help files in your computer for setting up the network. What operating system are you using? You can find help files in the Network Connections or Network area in your control panel.
i have two computers but only one of them has internet and i would like to have them both have internet but i dont want to pay for someone to come out and hook the other one up for me. i have a router but i dont know what to do. i am not good with computers so i need ALOT of help

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