So installing wifi basically means setting up all your devices; computer, router, to work together so you can create a wireless network to share files and go on the internet. To do that, you will first have to own a wireless enabled device, which is in this case my laptop which has wireless built in. If it didn't have wireless built in, I could use something like this, a wireless adapter I can connect to the USB port to give my computer a new wireless adapter to connect to the network.
The second thing you need is a working internet connection. DSL, or cable internet that comes with a modem. To that modem we'll attach something like this; a wireless router. This router will basically take the internet signal from the modem and share it with all our computers. The other thing the router will do is let the computers share information on their own. If you have a printer you would like to share, or files in a folder that's important for everybody in the house or office, you can share them all wireless with a a router.
And that's how you set up wifi.