Facebook v6.0.22 RTW with official support for Windows 8 and .NET 4.5 released. The Facebook C# SDK helps .Net developers build web, desktop, phone and metro style applications that integrate with Facebook.
In order to use this SDK with your C# solutions you have the following options.
You can get Facebook C# SDK source from Github and build use the libraries on your own (see Building Facebook C# SDK from Source), and you may also have to read Facebook developer documentation. (Official documentation from Facebook)
You can like and follow the updates about Facebook C# SDK @ Facebook page https://www.facebook.com/csharpsdk .
I hope this helps with your development.