Download SDK

http://facebooktoolkit.codeplex.com/

Extract the dlls and add reference to your asp.net web project.

Edit Web.config and add appSettings section and add following details

Drive main page from CanvasFBMLBasePage and set the base.RequireLogin property to true, to restrict user of the application to login to facebook before using your application.

Now u can use any API method to do whatever u want

Remember to remove html and body tag from .aspx page