what is silverlight how it can be linked with C#

Silverlight: previously known as WPF/E (where E means Everywhere), Silverlight is a cut down cross-platform version of WPF and is a browser plugin that lets you run rich internet applications, including media, animation and games.Silverlight allows applications to be written in any .NET language. For example c# and VB.NET. Silverlight will run on most popular platforms unlike winforms.

Here's a nice beginners guide to get you started as well.
http://code.msdn.microsoft.com/silverlight/Beginners-Guide-to-5a030b89[^]

I see that the question you are really asking is how would you get started with Silverlight. Well, first of all you are going to need the Silverlight SDK and a version of Visual Studio you can write Silverlight applications in.

If you go to this[^] page, you can find the links you need to download the latest version of Silverlight and the SDK, as well as links to Visual Studio.

I would suggest that you read and watch the tutorials available on the Silverlight site to get a basic understanding. When you want to go further, there are numerous excellent tutorials here on Code Project.