How do I install a computer cable?

Which cable are you refering to? I'll assume you're refering to the Network cable.

You can strech a long cable from the room that has the connection, either by putting it on the floor or tieing it nicely to the wall. another option is to install a WiFi card in the computer (If you have WiFi abilities in the network).

Going with the same assumption.  If you need a phone connection you can add a phone jack ( available at most electronic stores and I got one at walmarts) this connects to a phone in one room and you now have a phone via the wireless jack (goes into a power outlet). So you can go on line.  If you have wireless( cable or satellite) you can get a wireless router and a wireless adapter/booster I have a usb one (flash drive look to it). This will pick up the signal from anywhere in the house. With either one you can now have your computer in any room in the house.