Download the Wishield library.
Put it in the library folder on your machine. This is os dependant so check the instructiuons for location.
Change the library type in apps-conf.h check the documentation for the type you want.
I should imagine APP_WEBLIENT is what you will need.
Have a look at the client examples provided with the WiShield library.
Choose one and change the ip address, netmask and gateway for your network.
Specify the security type, inrastructure mode, ssid and passphrase or wep key as appropriate.
You may need to change the ip address of the web site.
Ping google.com you should get something like 209.85.227.103 and use the address.
I assume you know how to compile and load the sketch on to the arduino with wishield attached.
Start the serial monitor and set it to the correct speed as set in the sketch.
And there you go after a short while the red light will come on and you will get the results in the serial monitor.
This is all in the documentation if you read through it a few times to make sure you inderstand it.
Gordon