I just got my Wifi shield, and bought a wireless adapter for it (https://www.amazon.com/gp/product/B007R9U1QA/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1), and I am using the Wifi server code. The output I get is "WiFi shield not present". How do I get this to work?
I'm confused. You say you have a "WiFi Shield" and you bought an XBee-style radio to 'adapt' it. the "Arduino WiFi Shield" and "Arduino WiFi Shield 101" don't take a separate radio module. Also, the radio you got is a ZigBee Mesh radio, not a WiFi radio.
I suspect that what you have is not an "Arduino WiFi Shield" or "Arduino WiFi Shield 101". Does your board look like this one: https://www.arduino.cc/en/Main/ArduinoWiFiShield or like this one: https://www.arduino.cc/en/Main/ArduinoWiFiShield101 ?
It says on it "Wireless SD Shield". It is made by arduino.
Yes.
To use that for WiFi you will have to buy a WiFi module for it and find a library that will talk to that WiFi module. It will not be compatible with the Arduino WiFi Shield so you won't be able to use the built-in WiFi library or example sketches.
The official Digi (maker of XBee) WiFi module is: https://www.digi.com/products/xbee-rf-solutions/embedded-rf-modules-modems/xbee-wi-fi