Hi everyone, I'm new here.
I would like to ask about the function of the XBee.
Could it be used as a WiFi controller?
If not, which Arduino is suitable for me to control a device using WiFi/Bluetooth/Android?
Thanks a lot if you are willing to help me to solve my problem 
callmegill:
I would like to ask about the function of the XBee.
Could it be used as a WiFi controller?
No, XBee is completely different from WiFi.
If not, which Arduino is suitable for me to control a device using WiFi/Bluetooth/Android?
Which? WiFi and Bluetooth are completely different wireless protocols, and Android is an operating system mostly used for smartphones and tablets.
Pretty much any Arduino, with the appropriate accessories, can communicate using WiFi and/or Bluetooth. A bit more detail about what you're wanting to do might result in a more useful answer.
Also, keep in mind that Bluetooth has a range of only a few meters. A WiFi network can cover an area of tens/hundred meters, depending on your wireless router. WiFi gives you access to the internet, unlike Bluetooth.
Well, WiFi can give you access to the Internet, if it's connected to the Internet. Or it can be purely local. I'd expect there would be a way to access the Internet over Bluetooth as well (it can emulate a serial port, so there's always SLIP/PPP), but it's not commonly done.
XBee is not wifi-compatible, as others have noted, but there are several wifi,
BT, and other modules that plug directly into the XBee sockets and are
controllable from the Arduino RS232 port. So, you can buy a couple of XBee
shields, and try out several different types of communications.
http://rovingnetworks.com/products/RN_XV