How do I make a call to the Facebook API server from my desktop app?
Generally speaking, you prepare a request and then transmit it to the API server (see http://api.facebook.com/restserver.php) using POST over the HTTP protocol. The server will return an XML response.
You could write your own code to manage the Facebook session and handle the server communication, but you might want to leverage the excellent work other people have been doing and use one of these libraries instead:
Facebook and Microsoft have partnered to provide a Facebook Developer Kit built on Popfly and Visual Studio Express. You can get more information and downloads at http://www.microsoft.com/express/samples/facebook/. Even more information is available on CodePlex at http://www.codeplex.com/FacebookToolkit. An alternate library, Facebook.NET, which includes support for C# and VB.NET, can be found on CodePlex at http://www.codeplex.com/FacebookNET.
The facebook-actionscript-api is an MIT-licensed library for secure communication between Flash/Flex apps and the Facebook server, written and maintained by Jason Crist. More information and downloads are available at http://code.google.com/p/facebook-actionscript-api/.
Facebook used to provide an official Java Client Library, but it has subsequently been discontinued. The facebook-java-api project has taken over with an open source version, which you can download at http://code.google.com/p/facebook-java-api/ ...