Do shoot me, but a good resource for wifi is found here:
http://wifi.aximsite.com
Ikehiker took a great deal of time putting this together. I often refer to it myself.
To answer about it being like a radio tuner. Kinda, but not really, depending on where you live, you may or may not see any signals. In order to pick up a WiFi signal that enables you to connect to the internet, your work or office must have a WAP (Wireless Access Point). From here ike's guide can help you greatly.
As for stray wifi signals, unless you live in a fairly large city that is not technology challanged(like mine), you most likely see no stray signals. (except a neighbor's WAP, etc)