Wifi is something you buy yourself. Cable you buy from a company. There is usually a single cable company in your area so you don't have a choice there. Comcast is the major cable company and they provide cable and internet service. They install it all and get it working for you.

For wireless, then you go to your favorite computer store, and get a "wireless router." There are three or four major brands there like D-Link, Linksys and Netgear. For what you want, they all work just the same. Setting them up can take a bit of work for someone who doesn't know much about the product. So you may want to ask a family member who understands computers to help you. Otherwise, get services of BestBuy Geeksquad or equiv.

Once there, you also need to configure your PC to use it which the above resources can help with.

Hope this at least get you started :).