The only  major difference between using Silverlight with ASP.NET and normal ASP.NET development is that instead of using HTML for the presentation, you’re going to use XAML.

The core functionality of Silverlight is provided by a browser plug-in that renders XAML and exposes its internal Document Object Model (DOM) and event programming model to the browser in a way that is scriptable via JavaScript.

The below pic show the architecture of silverlight.

Hope,this will help to understand Silverlight.

Happy Coding.