how do I check to see if my wifi is working?

What other devices do you have? If you go to the place to pick the wifi network you want to connect to (which would differ depending on the device) do you see the name of your network? 

Also, what kind of router or gateway do you have? 

Last, check for a wireless on/off button on the router/gateway. Some have buttons which disable wireless, which might explain your problem.

@willia

Does the computer that's working use the wifi?  If so I'd say the wifi is working at least.  You can try connecting to the router using the info on the label on the bottom and see if that works for the other devices.